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Notes/01_Introduction/01_Python.md
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@@ -1,12 +1,10 @@
# 1.1 Python
In this part, we'll start with the absolute basics of Python.
### What is Python?
Python is an interpreted high level programming language. It is often classified as a
["scripting language"](https://en.wikipedia.org/wiki/Scripting_language) and
is considered to be similar to languages such as Perl, Tcl, or Ruby. The syntax
is considered similar to languages such as Perl, Tcl, or Ruby. The syntax
of Python is loosely inspired by elements of C programming.
Python was created by Guido van Rossum around 1990 who named it in honor of Monty Python.
@@ -14,12 +12,12 @@ Python was created by Guido van Rossum around 1990 who named it in honor of Mont
### Where to get Python?
[Python.org](https://www.python.org/) is where you obtain Python. For the purposes of this course, you
only need a basic installation. We recommend installing Python 3.6 or newer. We will be using Python3 in
our solutions and notes.
only need a basic installation. I recommend installing Python 3.6 or newer. Python 3.6 is used in the notes
and solutions.
### Why was Python created?
According to Guido:
In the words of Python's creator:
> My original motivation for creating Python was the perceived need
> for a higher level language in the Amoeba [Operating Systems]
@@ -34,9 +32,9 @@ According to Guido:
### Where is Python on my Machine?
Although there are many environments in which you might run Python,
this course has you run Python programs from the terminal or command
shell. From the terminal, you should be able to type a command such as
this:
Python is typically installed on your machine as a program that runs
from the terminal or command shell. From the terminal, you should be
able to type `python` like this:
```
bash $ python
@@ -51,15 +49,15 @@ hello world
If you are new to using the shell or a terminal, you should probably
stop, finish a short tutorial on that first, and then return here.
Just so you know, you will become a much better Python programmer if
you are able to run, debug, and interact with Python at the terminal
shell. This is Python's native environment. If you are able to use
Python in the shell, you will be able to use virtually everywhere
else.
Although there are many non-shell environments where you can code
Python, you will be a stronger Python programmer if you are able to
run, debug, and interact with Python at the terminal. This is
Python's native environment. If you are able to use Python here, you
will be able to use it everywhere else.
## Exercises
### (a) Using Python as a Calculator
### Exercise 1.1: Using Python as a Calculator
On your machine, start Python and use it as a calulator to solve the
following problem.
@@ -85,7 +83,7 @@ broker takes their 20% cut?
>>>
```
### (b) Getting help
### Exercise 1.2: Getting help
Use the `help()` command to get help on the `abs()` function. Then use
`help()` to get help on the `round()` function. Type `help()` just by
@@ -101,18 +99,19 @@ Followup: Go to <http://docs.python.org> and find the documentation for
the `abs()` function (hint: it’s found under the library reference
related to built-in functions).
### (c) Cutting and Pasting
### Exercise 1.3: Cutting and Pasting
As you've noticed, this course is structured as a series of traditional
web pages where you are encouraged to try interactive code samples by typing them
by hand. If you are learning Python for the first time, this is encouraged.
You will get a better feel for the language by slowing down, typing things in,
and thinking about what you are doing.
This course is structured as a series of traditional web pages where
you are encouraged to try interactive Python code samples **by typing
them out by hand.** If you are learning Python for the first time,
this "slow approach" is encouraged. You will get a better feel for
the language by slowing down, typing things in, and thinking about
what you are doing.
If you are inclined to use "cut and paste" in the editor, select code
If you must "cut and paste" code samples, select code
starting after the `>>>` prompt and going up to, but not any further
than the first blank line or the next `>>>` prompt (whichever appears
first). Select "copy" from the brower, go to the Python window, and
first). Select "copy" from the browser, go to the Python window, and
select "paste" to copy it into the Python shell. To get the code to
run, you may have to hit "Return" once after you’ve pasted it in.
@@ -139,12 +138,14 @@ Warning: It is never possible to paste more than one Python command
(statements that appear after `>>>`) to the basic Python shell at a
time. You have to paste each command one at a time.
### (d) Where is My Bus?
Now that you've done this, just remember that you will get more out of
the class by typing in code slowly and thinking about it--not cut and pasting.
If you’ve made it this far, try something more advanced and type these
statements to find out how long people waiting on the corner of Clark
street and Balmoral in Chicago will have to wait for the next
northbound CTA \#22 bus:
### Exercise 1.4: Where is My Bus?
Try something more advanced and type these statements to find out how
long people waiting on the corner of Clark street and Balmoral in
Chicago will have to wait for the next northbound CTA \#22 bus:
```pycon
>>> import urllib.request
@@ -181,5 +182,8 @@ exercise work. For example:
>>>
```
If you can't make this work, don't worry about it. The rest of this course
has nothing to do with parsing XML.
[Contents](../Contents) \| [Next (1.2 A First Program)](02_Hello_world)

92
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@@ -1,13 +1,14 @@
# 1.2 A First Python Program
# 1.2 A First Program
This section discusses the creation of your first program, running the interpreter,
and some basic debugging.
This section discusses the creation of your first program, running the
interpreter, and some basic debugging.
### Running Python
Python programs run inside an interpreter.
Python programs always run inside an interpreter.
The interpreter is a simple "console-based" application that normally starts from a command shell.
The interpreter is a "console-based" application that normally runs
from a command shell.
```bash
python3
@@ -18,15 +19,16 @@ Type "help", "copyright", "credits" or "license" for more information.
```
Expert programmers usually have no problem using the interpreter in
this way, but it's not so user-friendly for beginners. That said,
you'll become a better Python programmer if you're able to use the
interpreter from the shell earlier rather than later.
this way, but it's not so user-friendly for beginners. You may be using
an environment that provides a different interface to Python. That's fine,
but learning how to run Python terminal is still a useful skill to know.
### Interactive Mode
When you start Python, you get an *interactive* mode where you can experiment.
If you start typing statements, they will run immediately. There is no edit/compile/run/debug cycle.
If you start typing statements, they will run immediately. There is no
edit/compile/run/debug cycle.
```python
>>> print('hello world')
@@ -44,12 +46,12 @@ hello world
>>>
```
This *read-eval* loop is very useful for debugging and exploration.
This so-called *read-eval* loop is very useful for debugging and exploration.
Let's take a closer look at the elements:
- `>>>` is the interpreter prompt for starting a new statement.
- `...` is the interpreter prompt for continuing a statements. Enter a blank like to finish typing and run the statements.
- `...` is the interpreter prompt for continuing a statements. Enter a blank line to finish typing and run the statements.
The `...` prompt may or may not be shown depending on how you are using Python. For this course,
it is shown as blanks to make it easier to cut/paste code samples.
@@ -68,26 +70,6 @@ The underscore `_` holds the last result.
*This is only true in the interactive mode.* You never use `_` in a program.
Type `help(command)` to get information about `command`. Type `help()` with no name for interactive help.
```code
>>> help(range)
Help on class range in module builtins:
class range(object)
| range(stop) -> range object
| range(start, stop[, step]) -> range object
|
| Return an object that produces a sequence of integers from start (inclusive)
| to stop (exclusive) by step. range(i, j) produces i, i+1, i+2, ..., j-1.
| start defaults to 0, and stop is omitted! range(4) produces 0, 1, 2, 3.
| These are exactly the valid indices for a list of 4 elements.
| When step is given, it specifies the increment (or decrement).
```
The official documentation is at [http://docs.python.org](http://docs.python.org).
### Creating programs
Programs are put in `.py` files.
@@ -105,7 +87,7 @@ To execute a program, run it in the terminal with the `python` command.
For example, in command-line Unix:
```bash
bash % python3 hello.py
bash % python hello.py
hello world
bash %
```
@@ -124,9 +106,9 @@ Note: On Windows, you may need to specify a full path to the Python interpreter
### A Sample Program
Let's begin this part by trying to solve the following problem:
Let's solve the following problem:
> One morning, you go out and place a dollar bill on the sidewalk by the Sears tower.
> One morning, you go out and place a dollar bill on the sidewalk by the Sears tower in Chicago.
> Each day thereafter, you go out double the number of bills.
> How long does it take for the stack of bills to exceed the height of the tower?
@@ -149,7 +131,7 @@ print('Number of bills', num_bills)
print('Final height', num_bills * bill_thickness)
```
When we run it, we have the solution.
When you run it, you get the following output:
```bash
bash % python3 sears.py 1 1 0.00011
@@ -163,7 +145,7 @@ bash % python3 sears.py 1 1 0.00011
22 2097152 230.68672 Number of days 23 Number of bills 4194304 Final height 461.37344
```
Using this program as a guide, you can learn a few core concepts about Python.
Using this program as a guide, you can learn a number of important core concepts about Python.
### Statements
@@ -175,7 +157,7 @@ b = a * 2
print(b)
```
Each statement is terminated by a newline. Statements are executed one after the other until you reach the end of the file.
Each statement is terminated by a newline. Statements are executed one after the other until control reaches the end of the file.
### Comments
@@ -235,8 +217,7 @@ WHILE x < 0: # ERROR
### Looping
Looping is a way to execute a set of instructions any number of times.
There are many ways to accomplish this in Python, one of them is the `while` statement:
The `while` statement executes a loop.
```python
while num_bills * bill_thickness < sears_height:
@@ -252,7 +233,7 @@ The statements below the `while` will execute as long as the expression after th
### Indentation
Indentation in Python is used to denote a set of statements that go together.
From our previous example:
Consider the previous example:
```python
while num_bills * bill_thickness < sears_height:
@@ -263,7 +244,8 @@ while num_bills * bill_thickness < sears_height:
print('Number of days', days)
```
The indentation means that the following statements go together under the `while`.
Indentation groups the following statements together as the operations that
execute repeatedly:
```python
print(day, num_bills, num_bills * bill_thickness)
@@ -271,8 +253,8 @@ The indentation means that the following statements go together under the `while
num_bills = num_bills * 2
```
Because the next statement is not indented, it means that it does not
belong to the previous set. The empty line is just for
Because the `print()` statement at the end is not indented, it means
that it does not belong to the loop. The empty line is just for
readability. It does not affect the execution.
### Indentation best practices
@@ -281,7 +263,8 @@ readability. It does not affect the execution.
* Use 4 spaces per level.
* Use a Python-aware editor.
Indentation within the block must be consistent.
Python's only requirement is that indentation within the same block
be consistent. For example, this is an error:
```python
while num_bills * bill_thickness < sears_height:
@@ -290,7 +273,6 @@ while num_bills * bill_thickness < sears_height:
num_bills = num_bills * 2
```
### Conditionals
The `if` statement is used to execute a conditional:
@@ -306,7 +288,7 @@ else:
Depending on the values of `a` and `b`, the execution will jump to `print('Computer says no')` or `print('Computer says yes')`.
You can check for multiple conditions with the `elif`.
You can check for multiple conditions by adding extra checks using `elif`.
```python
if a > b:
@@ -335,14 +317,14 @@ x = 100
print(x) # Prints the text '100'
```
If you pass more than one item to `print` they are separated by spaces.
If you pass more than one value to `print` they are separated by spaces.
```python
name = 'Jake'
print('My name is', name) # Print the text 'My name is Jake'
```
`print()` always creates a new line at the end.
`print()` always puts a new line at the end.
```python
print('Hello')
@@ -356,14 +338,14 @@ Hello
My name is Jake
```
This can be avoided.
The extra newline can be suppressed:
```python
print('Hello', end=' ')
print('My name is', 'Jake')
```
The previous code will print:
This code will now print:
```code
Hello My name is Jake
@@ -378,13 +360,13 @@ name = input('Enter your name:')
print('Your name is', name)
```
`input` prints a prompt to the user and returns the response.
`input` prints a prompt to the user and returns their response.
This is useful for small programs, learning exercises or simple debugging.
It is not widely used for real programs.
### `pass` statement
Sometimes you need to specify an empty block. The keyword `pass` is used for it.
Sometimes you need to specify an empty code block. The keyword `pass` is used for it.
```python
if a > b:
@@ -393,11 +375,11 @@ else:
print('Computer says false')
```
This is also called a "no-op" statement. It does nothing. It serves as a placeholder for statements. Possibly to be added later.
This is also called a "no-op" statement. It does nothing. It serves as a placeholder for statements, possibly to be added later.
## Exercises
### (a) The Bouncing Ball
### Exercise 1.5: The Bouncing Ball
A rubber ball is dropped from a height of 100 meters and each time it hits the ground, it bounces back up to 3/5 the height it fell.
Write a program "bounce.py" that prints a table showing the height of the first 10 bounces.
@@ -432,7 +414,7 @@ Your program should make a table that looks something like this:
10 0.6047
```
### (b) Debugging
### Exercise 1.6: Debugging
The following code fragment contains code from the Sears tower problem. It also has a bug in it.

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@@ -1,7 +1,5 @@
# 1.3 Numbers
This section covers some basics of performing mathematical calculations in Python.
### Types of Numbers
Python has 4 types of numbers:
@@ -11,7 +9,7 @@ Python has 4 types of numbers:
* Floating point
* Complex (imaginary numbers)
### Booleans
### Booleans (bool)
Booleans have two values: `True`, `False`.
@@ -29,9 +27,9 @@ if d == 0:
print('d is False')
```
*Don't do that, it would be odd.*
*Don't write code like that. It would be odd.*
### Integers
### Integers (int)
Signed values of arbitrary size and base:
@@ -62,26 +60,6 @@ x ^ y Bit-wise XOR
abs(x) Absolute value
```
### Comparisons
The following comparison / relational operators work with numbers:
`<`, `>`, `<=` `>=`, `==`, `!=`
You can form more complex boolean expressions using
`and`, `or`, `not`
Here are a few examples:
```python
if b >= a and b <= c:
print('b is between a and c')
if not (b < a or b > c):
print('b is still between a and c')
```
### Floating point (float)
Use a decimal or exponential notation to specify a floating point value:
@@ -136,6 +114,34 @@ d = math.tan(x)
e = math.log(x)
```
### Comparisons
The following comparison / relational operators work with numbers:
```
x < y Less than
x <= y Less than or equal
x > y Greater than
x >= y Greater than or equal
x == y Equal to
x != y Not equal to
```
You can form more complex boolean expressions using
`and`, `or`, `not`
Here are a few examples:
```python
if b >= a and b <= c:
print('b is between a and c')
if not (b < a or b > c):
print('b is still between a and c')
```
### Converting Numbers
The type name can be used to convert values:
@@ -159,7 +165,7 @@ Try it out.
## Exercises
### (a) Dave's mortgage
### Exercise 1.7: Dave's mortgage
Dave has decided to take out a 30-year fixed rate mortgage of $500,000 with Guido’s Mortgage, Stock Investment, and Bitcoin trading corporation.
The interest rate is 5% and the monthly payment is $2684.11.
@@ -183,7 +189,7 @@ print('Total paid', total_paid)
Enter this program and run it. You should get an answer of `966,279.6`.
### (b) Extra payments
### Exercise 1.8: Extra payments
Suppose Dave pays an extra $1000/month for the first 12 months of the mortgage?
@@ -191,7 +197,7 @@ Modify the program to incorporate this extra payment and have it print the total
When you run the new program, it should report a total payment of `929,965.62` over 342 months.
### (c) Making an Extra Payment Calculator
### Exercise 1.9: Making an Extra Payment Calculator
Modify the program so that extra payment information can be more generally handled.
Make it so that the user can set these variables:
@@ -206,7 +212,7 @@ Make the program look at these variables and calculate the total paid appropriat
How much will Dave pay if he pays an extra $1000/month for 4 years starting in year 5 of the mortgage?
### (d) Making a table
### Exercise 1.10: Making a table
Modify the program to print out a table showing the month, total paid so far, and the remaining principal.
The output should look something like this:
@@ -224,8 +230,28 @@ Total paid 878389.99
Months 309
```
### (e) Bonus
### Exercise 1.11: Bonus
While you’re at it, fix the program to correct the for overpayment that occurs in the last month.
### Exercise 1.12: A Mystery
`int()` and `float()` can be used to convert numbers. For example,
```pycon
>>> int("123")
123
>>> float("1.23")
1.23
>>>
```
With that in mind, can you explain this behavior?
```pycon
>>> bool("False")
True
>>>
```
[Contents](../Contents) \| [Previous (1.2 A First Program)](02_Hello_world) \| [Next (1.4 Strings)](04_Strings)

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@@ -1,7 +1,5 @@
# 1.4 Strings
This section covers the basics of text manipulation.
### Representing Text
String are text literals written in programs with quotes.
@@ -40,9 +38,8 @@ at the keyboard. Here are some common escape codes:
### String Representation
Each character represents a raw unicode code point.
<!-- TODO: Add Picture of following characters -->
The characters in a string are Unicode and represent a so-called "code-point". You can
specify an exact code-point using the following escape sequences:
```python
a = '\xf1' # a = 'ñ'
@@ -51,7 +48,12 @@ c = '\U0001D122' # c = '𝄢'
d = '\N{FORALL}' # d = '∀'
```
Strings work like an array for accessing its characters. You use an integer index, starting at 0.
The [Unicode Character Database](https://unicode.org/charts) is a reference for all
available character codes.
### String Indexing
Strings work like an array for accessing individual characters. You use an integer index, starting at 0.
```python
a = 'Hello world'
@@ -85,7 +87,7 @@ len(s) # 5
# Membership test (`in`, `not in`)
t = 'e' in s # True
f = 'x' in s # False
tt = 'hi' not in s # True
g = 'hi' not in s # True
# Replication (s * n)
rep = s * 5 # 'HelloHelloHelloHelloHello'
@@ -95,14 +97,14 @@ rep = s * 5 # 'HelloHelloHelloHelloHello'
Strings have methods that perform various operations with the string data.
Stripping any leading / trailing white space.
Example: stripping any leading / trailing white space.
```python
s = ' Hello '
t = s.strip() # 'Hello'
```
Case conversion.
Example: Case conversion.
```python
s = 'Hello'
@@ -110,7 +112,7 @@ l = s.lower() # 'hello'
u = s.upper() # 'HELLO'
```
Replacing text.
Example: Replacing text.
```python
s = 'Hello world'
@@ -119,7 +121,8 @@ t = s.replace('Hello' , 'Hallo') # 'Hallo world'
**More string methods:**
Strings have a wide variety of other methods for testing and manipulating the text data:
Strings have a wide variety of other methods for testing and manipulating the text data.
This is small sample of methods:
```python
s.endswith(suffix) # Check if string ends with suffix
@@ -158,7 +161,7 @@ TypeError: 'str' object does not support item assignment
### String Conversions
Use `str()` to convert a value to a string.
Use `str()` to convert any value to a string suitable for printing.
```python
>>> x = 42
@@ -169,13 +172,13 @@ Use `str()` to convert a value to a string.
### Byte Strings
A string of 8-bit bytes.
A string of 8-bit bytes, commonly encountered with low-level I/O.
```python
data = b'Hello World\r\n'
```
By putting a little b before our string literal we specify that it is a byte string as opposed to a text string.
By putting a little b before the first quotation, you specify that it is a byte string as opposed to a text string.
Most of the usual string operations work.
@@ -185,13 +188,13 @@ data[0:5] # b'Hello'
data.replace(b'Hello', b'Cruel') # b'Cruel World\r\n'
```
Indexing is a bit different because it returns byte values.
Indexing is a bit different because it returns byte values as integers.
```python
data[0] # 72 (ASCII code for 'H')
```
Conversion to/from text.
Conversion to/from text strings.
```python
text = data.decode('utf-8') # bytes -> text
@@ -200,7 +203,7 @@ data = text.encode('utf-8') # text -> bytes
### Raw Strings
Raw strings are strings with uninterpreted backslash. They are little by prefixing the initial quote with a lowercase "r".
Raw strings are string literals with an uninterpreted backslash. They specified by prefixing the initial quote with a lowercase "r".
```python
>>> rs = r'c:\newdata\test' # Raw (uninterpreted backslash)
@@ -208,8 +211,9 @@ Raw strings are strings with uninterpreted backslash. They are little by prefix
'c:\\newdata\\test'
```
The string is the literal text, exactly as typed.
This is useful in situations where the backslash has special significance. Example: filename, regular expressions, etc.
The string is the literal text enclosed inside, exactly as typed.
This is useful in situations where the backslash has special
significance. Example: filename, regular expressions, etc.
### f-Strings
@@ -228,13 +232,13 @@ A string with formatted expression substitution.
>>>
```
**Note: This requires Python 3.6 or newer.**
**Note: This requires Python 3.6 or newer.** The meaning of the format codes
is covered later.
## Exercises
In this exercise, we experiment with operations on Python's string type.
You may want to do most of this exercise at the Python interactive prompt where you can easily see the results.
In these exercises, you experiment with operations on Python's string type.
You should do this at the Python interactive prompt where you can easily see the results.
Important note:
> In exercises where you are supposed to interact with the interpreter,
@@ -251,7 +255,7 @@ Start by defining a string containing a series of stock ticker symbols like this
>>>
```
### (a): Extracting individual characters and substrings
### Exercise 1.13: Extracting individual characters and substrings
Strings are arrays of characters. Try extracting a few characters:
@@ -269,7 +273,7 @@ Strings are arrays of characters. Try extracting a few characters:
>>>
```
### (b) Strings as read-only objects
### Exercise 1.14: Strings as read-only objects
In Python, strings are read-only.
@@ -283,7 +287,7 @@ TypeError: 'str' object does not support item assignment
>>>
```
### (c) String concatenation
### Exercise 1.15: String concatenation
Although string data is read-only, you can always reassign a variable
to a newly created string.
@@ -298,7 +302,7 @@ the end of `symbols`:
>>>
```
Oops! That's not what we wanted. Fix it so that the `symbols` variable holds the value `'HPQ,AAPL,IBM,MSFT,YHOO,SCO,GOOG'`.
Oops! That's not what you wanted. Fix it so that the `symbols` variable holds the value `'HPQ,AAPL,IBM,MSFT,YHOO,SCO,GOOG'`.
In these examples, it might look like the original string is being
modified, in an apparent violation of strings being read only. Not
@@ -307,15 +311,16 @@ time. When the variable name `symbols` is reassigned, it points to the
newly created string. Afterwards, the old string is destroyed since
it's not being used anymore.
### (d) Membership testing (substring testing)
### Exercise 1.16: Membership testing (substring testing)
Experiment with the `in` operator to check for substrings. At the interactive prompt, try these operations:
Experiment with the `in` operator to check for substrings. At the
interactive prompt, try these operations:
```pycon
>>> 'IBM' in symbols
?
>>> 'AA' in symbols
?
True
>>> 'CAT' in symbols
?
>>>
@@ -323,7 +328,7 @@ Experiment with the `in` operator to check for substrings. At the interactive p
*Why did the check for "AA" return `True`?*
### (e) String Methods
### Exercise 1.17: String Methods
At the Python interactive prompt, try experimenting with some of the string methods.
@@ -359,7 +364,7 @@ Try some more operations:
>>>
```
### (f) f-strings
### Exercise 1.18: f-strings
Sometimes you want to create a string and embed the values of
variables into it.
@@ -375,13 +380,15 @@ To do that, use an f-string. For example:
>>>
```
Modify the `mortgage.py` program from Exercise 1.3 to create its output using f-strings.
Modify the `mortgage.py` program from [Exercise 1.10](03_Numbers) to create its output using f-strings.
Try to make it so that output is nicely aligned.
### Commentary
As you start to experiment with the interpreter, you often want to know more about the operations supported by different objects.
For example, how do you find out what operations are available on a string?
As you start to experiment with the interpreter, you often want to
know more about the operations supported by different objects. For
example, how do you find out what operations are available on a
string?
Depending on your Python environment, you might be able to see a list
of available methods via tab-completion. For example, try typing
@@ -399,7 +406,12 @@ builtin-in `dir()` function. For example:
```python
>>> s = 'hello'
>>> dir(s)
['__add__', '__class__', '__contains__', ..., 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']
['__add__', '__class__', '__contains__', ..., 'find', 'format',
'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace',
'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition',
'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit',
'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase',
'title', 'translate', 'upper', 'zfill']
>>>
```
@@ -417,9 +429,4 @@ upper(...)
>>>
```
IDEs and alternative interactive shells often give you more help here.
For example, a popular alternative to Python's normal interactive mode
is IPython (http://ipython.org). IPython provides some nice features
such as tab-completion of method names, more integrated help and more.
[Contents](../Contents) \| [Previous (1.3 Numbers)](03_Numbers) \| [Next (1.5 Lists)](05_Lists)

35
Notes/01_Introduction/05_Lists.md
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@@ -1,10 +1,8 @@
# 1.5 Lists
This section introduces lists, one of Python's basic objects for storing collections of data.
### Creating a List
Use square brackets to create a list:
Use square brackets to define a list:
```python
names = [ 'Elwood', 'Jake', 'Curtis' ]
@@ -55,7 +53,7 @@ Negative indices count from the end.
names[-1] # 'Curtis'
```
You can change on element in the list.
You can change any item in the list.
```python
names[1] = 'Joliet Jake'
@@ -96,20 +94,20 @@ for name in names:
This is similar to a `foreach` statement from other programming languages.
To find something quickly, use `index()`.
To find the position of something quickly, use `index()`.
```python
names = ['Elwood','Jake','Curtis']
names.index('Curtis') # 2
```
If the element is present more than one, it will return the index of the first occurrence.
If the element is present more than once, `index()` will return the index of the first occurrence.
If the element is not found, it will raise a `ValueError` exception.
### List Removal
You can remove either with the element value or the index number.
You can remove items either by element value or by index:
```python
# Using the value
@@ -119,12 +117,12 @@ names.remove('Curtis')
del names[1]
```
Removing results in items moving down to fill the space vacated. There are no holes in the list.
Removing an item does not create a hole. Other items will move down to fill the space vacated.
If there are more than one occurrence of the element, `.remove()` will remove only the first occurrence.
### List Sorting
Lists can be sorted 'in-place'.
Lists can be sorted "in-place".
```python
s = [10, 1, 7, 3]
@@ -152,11 +150,12 @@ s.sort() # ['bar', 'foo', 'spam']
```
Specifically, lists don't represent vectors/matrices as in MATLAB, Octave, IDL, etc.
However, there are some packages to help you with that (e.g. numpy).
However, there are some packages to help you with that (e.g. [numpy](https://numpy.org)).
## Exercises
In this exercise, we experiment with Python's list datatype. In the last exercise, you worked with strings containing stock symbols.
In this exercise, we experiment with Python's list datatype. In the last section,
you worked with strings containing stock symbols.
```pycon
>>> symbols = 'HPQ,AAPL,IBM,MSFT,YHOO,DOA,GOOG'
@@ -168,7 +167,7 @@ Split it into a list of names using the `split()` operation of strings:
>>> symlist = symbols.split(',')
```
### (a) Extracting and reassigning list elements
### Exercise 1.19: Extracting and reassigning list elements
Try a few lookups:
@@ -224,7 +223,7 @@ You can reassign a portion of a list to another list. For example:
When you do this, the list on the left-hand-side (`symlist`) will be resized as appropriate to make the right-hand-side (`mysyms`) fit.
For instance, in the above example, the last two items of `symlist` got replaced by the single item in the list `mysyms`.
### (b) Looping over list items
### Exercise 1.20: Looping over list items
The `for` loop works by looping over data in a sequence such as a list.
Check this out by typing the following loop and watching what happens:
@@ -235,7 +234,7 @@ Check this out by typing the following loop and watching what happens:
# Look at the output
```
### (c) Membership tests
### Exercise 1.21: Membership tests
Use the `in` or `not in` operator to check if `'AIG'`,`'AA'`, and `'CAT'` are in the list of symbols.
@@ -249,7 +248,7 @@ True
>>>
```
### (d) Appending, inserting, and deleting items
### Exercise 1.22: Appending, inserting, and deleting items
Use the `append()` method to add the symbol `'RHT'` to end of `symlist`.
@@ -319,7 +318,7 @@ Remove the first occurrence of `'YHOO'`.
Just so you know, there is no method to find or remove all occurrences of an item.
However, we'll see an elegant way to do this in section 2.
### (e) Sorting
### Exercise 1.23: Sorting
Want to sort a list? Use the `sort()` method. Try it out:
@@ -341,7 +340,7 @@ Want to sort in reverse? Try this:
Note: Sorting a list modifies its contents 'in-place'. That is, the elements of the list are shuffled around, but no new list is created as a result.
### (f) Putting it all back together
### Exercise 1.24: Putting it all back together
Want to take a list of strings and join them together into one string?
Use the `join()` method of strings like this (note: this looks funny at first).
@@ -359,7 +358,7 @@ Use the `join()` method of strings like this (note: this looks funny at first).
>>>
```
### (g) Lists of anything
### Exercise 1.25: Lists of anything
Lists can contain any kind of object, including other lists (e.g., nested lists).
Try this out:

30
Notes/01_Introduction/06_Files.md
View File

@@ -1,7 +1,5 @@
# 1.6 File Management
This section discusses the basics of working with files.
### File Input and Output
Open a file.
@@ -84,9 +82,10 @@ with open('outfile', 'wt') as f:
This exercise depends on a file `Data/portfolio.csv`. The file contains a list of lines with information on a portfolio of stocks.
Locate the file and look at its contents:
### (a) File Preliminaries
### Exercise 1.26: File Preliminaries
*Note: Make sure you are running Python in a location where you can access the `portfolio.csv` file.
It's normally located in `Data/portfolio.csv`.
You can find out where Python thinks it's running by doing this:
```pycon
@@ -115,9 +114,11 @@ name,shares,price
>>>
```
In the above example, it should be noted that Python has two modes of output.
In the first mode where you type `data` at the prompt, Python shows you the raw string representation including quotes and escape codes.
When you type `print(data)`, you get the actual formatted output of the string.
In the above example, it should be noted that Python has two modes of
output. In the first mode where you type `data` at the prompt, Python
shows you the raw string representation including quotes and escape
codes. When you type `print(data)`, you get the actual formatted
output of the string.
Although reading a file all at once is simple, it is often not the
most appropriate way to do it—especially if the file happens to be
@@ -137,9 +138,12 @@ name,shares,price
>>>
```
When you use this code as shown, lines are read until the end of the file is reached at which point the loop stops.
When you use this code as shown, lines are read until the end of the
file is reached at which point the loop stops.
On certain occasions, you might want to manually read or skip a *single* line of text (e.g., perhaps you want to skip the first line of column headers).
On certain occasions, you might want to manually read or skip a
*single* line of text (e.g., perhaps you want to skip the first line
of column headers).
```pycon
>>> f = open('Data/portfolio.csv', 'rt')
@@ -180,7 +184,7 @@ For example, try this:
*Note: In these examples, `f.close()` is being called explicitly because the `with` statement isn’t being used.*
### (b) Reading a data file
### Exercise 1.27: Reading a data file
Now that you know how to read a file, let’s write a program to perform a simple calculation.
@@ -197,10 +201,12 @@ Your program should print output such as the following:
Total cost 44671.15
```
### (c) Other kinds of 'files'
### Exercise 1.28: Other kinds of 'files'
What if you wanted to read a non-text file such as a gzip-compressed datafile?
The builtin `open()` function won’t help you here, but Python has a library module `gzip` that can read gzip compressed files.
What if you wanted to read a non-text file such as a gzip-compressed
datafile? The builtin `open()` function won’t help you here, but
Python has a library module `gzip` that can read gzip compressed
files.
Try it:

63
Notes/01_Introduction/07_Functions.md
View File

@@ -1,4 +1,4 @@
# 1.7 Introduction to Functions
# 1.7 Functions
As your programs start to get larger, you'll want to get organized. This section
introduces functions. Error handling with exceptions is also introduced.
@@ -41,14 +41,15 @@ x = math.sqrt(10)
# `urllib.request` module
import urllib.request
u = urllib.request.urlopen('http://www.python.org/') data = u.read()
u = urllib.request.urlopen('http://www.python.org/')
data = u.read()
```
We will cover libraries and modules in more detail later.
### Errors and exceptions
Errors are reported as exceptions. An exception causes the program to stop.
Functions report errors as exceptions. An exception causes the program to stop.
Try this in your python REPL.
@@ -60,13 +61,14 @@ ValueError: invalid literal for int() with base 10: 'N/A'
>>>
```
For debugging purposes, the message describes what happened, where the error occurred and the traceback.
For debugging purposes, the message describes what happened, where the error occurred,
and a traceback showing the other function calls that led to the failure.
### Catching and Handling Exceptions
Exceptions can be caught and handled.
To catch, use `try - except` statement.
To catch, use the `try - except` statement.
```python
for line in f:
@@ -88,7 +90,7 @@ To raise an exception, use the `raise` statement.
raise RuntimeError('What a kerfuffle')
```
This will cause the program to abord with an exception traceback. Unless caught by a `try-except` block.
This will cause the program to abort with an exception traceback. Unless caught by a `try-except` block.
```bash
% python3 foo.py
@@ -100,7 +102,7 @@ RuntimeError: What a kerfuffle
## Exercises
### (a) Defining a function
### Exercise 1.29: Defining a function
You can define a simple function using the `def` statement. For example,
@@ -119,12 +121,15 @@ Hello Paula
If the first statement of a function is a string, it serves as documentation.
Try typing a command such as `help(greeting)` to see it displayed.
### (b) Turning a script into a function
### Exercise 1.30: Turning a script into a function
Take the code you wrote for the `pcost.py` program in the last exercise and turn it into a function `portfolio_cost(filename)`.
The function takes a filename as input, reads the portfolio data in that file, and returns the total cost of the portfolio.
Take the code you wrote for the `pcost.py` program in [Exercise 1.27](06_Files)
and turn it into a function `portfolio_cost(filename)`. The
function takes a filename as input, reads the portfolio data in that
file, and returns the total cost of the portfolio as a float.
To use your function, change your program so that it looks something like this:
To use your function, change your program so that it looks something
like this:
```python
def portfolio_cost(filename):
@@ -137,7 +142,8 @@ print('Total cost:', cost)
```
When you run your program, you should see the same output as before.
After you’ve run your program, you can also call your function interactively by typing this:
After you’ve run your program, you can also call your function
interactively by typing this:
```bash
bash $ python3 -i pcost.py
@@ -151,7 +157,8 @@ This will allow you to call your function from the interactive mode.
>>>
```
Being able to experiment with your code interactively is useful for testing and debugging.
Being able to experiment with your code interactively is useful for
testing and debugging.
What happens if you try your function on a file with some missing fields?
@@ -170,14 +177,15 @@ you can either sanitize the original input file by eliminating bad
lines or you can modify your code to handle the bad lines in some
manner.
Modify the `pcost.py` program to catch the exception, print a warning message,
and continue processing the rest of the file.
Modify the `pcost.py` program to catch the exception, print a warning
message, and continue processing the rest of the file.
### (c) Using a library function
### Exercise 1.31: Using a library function
Python comes with a large standard library of useful functions.
One library that might be useful here is the `csv` module. You should use it whenever you have to work with CSV data files.
Here is an example of how it works:
Python comes with a large standard library of useful functions. One
library that might be useful here is the `csv` module. You should use
it whenever you have to work with CSV data files. Here is an example
of how it works:
```pycon
>>> import csv
@@ -200,12 +208,15 @@ Here is an example of how it works:
>>>
```
One nice thing about the `csv` module is that it deals with a variety of low-level details such as quoting and proper comma splitting.
In the above output, you’ll notice that it has stripped the double-quotes away from the names in the first column.
One nice thing about the `csv` module is that it deals with a variety
of low-level details such as quoting and proper comma splitting. In
the above output, you’ll notice that it has stripped the double-quotes
away from the names in the first column.
Modify your `pcost.py` program so that it uses the `csv` module for parsing and try running earlier examples.
Modify your `pcost.py` program so that it uses the `csv` module for
parsing and try running earlier examples.
### (d) Reading from the command line
### Exercise 1.32: Reading from the command line
In the `pcost.py` program, the name of the input file has been hardwired into the code:
@@ -221,9 +232,11 @@ cost = portfolio_cost('Data/portfolio.csv')
print('Total cost:', cost)
```
That’s fine for learning and testing, but in a real program you probably wouldn’t do that.
That’s fine for learning and testing, but in a real program you
probably wouldn’t do that.
Instead, you might pass the name of the file in as an argument to a script. Try changing the bottom part of the program as follows:
Instead, you might pass the name of the file in as an argument to a
script. Try changing the bottom part of the program as follows:
```python
# pcost.py