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Notes/03_Program_organization/01_Script.md
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# 3.1 Python Scripting # 3.1 Scripting
In this part we look more closely at the practice of writing Python In this part we look more closely at the practice of writing Python
scripts. scripts.
@@ -233,7 +233,7 @@ for row in report:
In this exercise, we’re going take this program and organize it a little more strongly around the use of functions. In this exercise, we’re going take this program and organize it a little more strongly around the use of functions.
### (a) Structuring a program as a collection of functions ### Exercise 3.1: Structuring a program as a collection of functions
Modify your `report.py` program so that all major operations, Modify your `report.py` program so that all major operations,
including calculations and output, are carried out by a collection of including calculations and output, are carried out by a collection of
@@ -242,7 +242,7 @@ functions. Specifically:
* Create a function `print_report(report)` that prints out the report. * Create a function `print_report(report)` that prints out the report.
* Change the last part of the program so that it is nothing more than a series of function calls and no other computation. * Change the last part of the program so that it is nothing more than a series of function calls and no other computation.
### (b) Creating a function for program execution ### Exercise 3.2: Creating a function for program execution
Take the last part of your program and package it into a single function `portfolio_report(portfolio_filename, prices_filename)`. Take the last part of your program and package it into a single function `portfolio_report(portfolio_filename, prices_filename)`.
Have the function work so that the following function call creates the report as before: Have the function work so that the following function call creates the report as before:
@@ -272,4 +272,4 @@ For example, try these statements interactively after running your program:
>>> >>>
``` ```
[Next](02_More_functions) [Contents](../Contents) \| [Previous (2.7 Object Model)](../02_Working_with_data/07_Objects) \| [Next (3.2 More on Functions)](02_More_functions)

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Notes/03_Program_organization/02_More_functions.md
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@@ -253,7 +253,7 @@ our goal.
Start this exercise by creating a new file called `fileparse.py`. This is where we will be doing our work. Start this exercise by creating a new file called `fileparse.py`. This is where we will be doing our work.
### (a) Reading CSV Files ### Exercise 3.3: Reading CSV Files
To start, let’s just focus on the problem of reading a CSV file into a To start, let’s just focus on the problem of reading a CSV file into a
list of dictionaries. In the file `fileparse.py`, define a simple list of dictionaries. In the file `fileparse.py`, define a simple
@@ -300,7 +300,7 @@ Hint: `python3 -i fileparse.py`.
This is great except that you can’t do any kind of useful calculation with the data because everything is represented as a string. This is great except that you can’t do any kind of useful calculation with the data because everything is represented as a string.
We’ll fix this shortly, but let’s keep building on it. We’ll fix this shortly, but let’s keep building on it.
### (b) Building a Column Selector ### Exercise 3.4: Building a Column Selector
In many cases, you’re only interested in selected columns from a CSV file, not all of the data. In many cases, you’re only interested in selected columns from a CSV file, not all of the data.
Modify the `parse_csv()` function so that it optionally allows user-specified columns to be picked out as follows: Modify the `parse_csv()` function so that it optionally allows user-specified columns to be picked out as follows:
@@ -318,7 +318,7 @@ Modify the `parse_csv()` function so that it optionally allows user-specified co
>>> >>>
``` ```
An example of a column selector was given in Section 2.5. An example of a column selector was given in [Exercise 2.23](../02_Working_with_data/06_List_comprehension).
However, here’s one way to do it: However, here’s one way to do it:
```python ```python
@@ -394,7 +394,7 @@ When you read a row of data from the file, the indices are used to filter it:
>>> >>>
``` ```
### (c) Performing Type Conversion ### Exercise 3.5: Performing Type Conversion
Modify the `parse_csv()` function so that it optionally allows type-conversions to be applied to the returned data. Modify the `parse_csv()` function so that it optionally allows type-conversions to be applied to the returned data.
For example: For example:
@@ -410,7 +410,7 @@ For example:
>>> >>>
``` ```
You already explored this in Exercise 2.7. You'll need to insert the You already explored this in [Exercise 2.24](../02_Working_with_data/07_Objects). You'll need to insert the
following fragment of code into your solution: following fragment of code into your solution:
```python ```python
@@ -420,7 +420,7 @@ if types:
... ...
``` ```
### (d) Working with Headers ### Exercise 3.6: Working with Headers
Some CSV files don’t include any header information. Some CSV files don’t include any header information.
For example, the file `prices.csv` looks like this: For example, the file `prices.csv` looks like this:
@@ -448,7 +448,7 @@ line of data isn’t interpreted as a header line. Also, you’ll need to
make sure you don’t create dictionaries as there are no longer any make sure you don’t create dictionaries as there are no longer any
column names to use for keys. column names to use for keys.
### (e) Picking a different column delimitier ### Exercise 3.7: Picking a different column delimitier
Although CSV files are pretty common, it’s also possible that you could encounter a file that uses a different column separator such as a tab or space. Although CSV files are pretty common, it’s also possible that you could encounter a file that uses a different column separator such as a tab or space.
For example, the file `Data/portfolio.dat` looks like this: For example, the file `Data/portfolio.dat` looks like this:
@@ -486,6 +486,4 @@ You can use it to parse arbitrary CSV files, select out columns of
interest, perform type conversions, without having to worry too much interest, perform type conversions, without having to worry too much
about the inner workings of files or the `csv` module. about the inner workings of files or the `csv` module.
Nice! [Contents](../Contents) \| [Previous (3.1 Scripting)](01_Script) \| [Next (3.3 Error Checking)](03_Error_checking)
[Next](03_Error_checking)

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Notes/03_Program_organization/03_Error_checking.md
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@@ -301,7 +301,7 @@ resources are released. `with` only works with certain objects.
## Exercises ## Exercises
### (a) Raising exceptions ### Exercise 3.8: Raising exceptions
The `parse_csv()` function you wrote in the last section allows The `parse_csv()` function you wrote in the last section allows
user-specified columns to be selected, but that only works if the user-specified columns to be selected, but that only works if the
@@ -336,7 +336,7 @@ headers, but simultaneously specifying that there are no headers).
This indicates a programming error on the part of the calling code. This indicates a programming error on the part of the calling code.
### (b) Catching exceptions ### Exercise 3.9: Catching exceptions
The `parse_csv()` function you wrote is used to process the entire The `parse_csv()` function you wrote is used to process the entire
contents of a file. However, in the real-world, it’s possible that contents of a file. However, in the real-world, it’s possible that
@@ -373,7 +373,7 @@ Row 7: Reason invalid literal for int() with base 10: ''
>>> >>>
``` ```
### (c) Silencing Errors ### Exercise 3.10: Silencing Errors
Modify the `parse_csv()` function so that parsing error messages can be silenced if explicitly desired by the user. Modify the `parse_csv()` function so that parsing error messages can be silenced if explicitly desired by the user.
For example: For example:
@@ -390,4 +390,4 @@ most programs. As a general rule, you shouldn’t silently ignore
errors. Instead, it’s better to report problems and to give the user errors. Instead, it’s better to report problems and to give the user
an option to the silence the error message if they choose to do so. an option to the silence the error message if they choose to do so.
[Next](04_Modules) [Contents](../Contents) \| [Previous (3.2 More on Functions)](02_More_functions) \| [Next (3.4 Modules)](04_Modules)

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Notes/03_Program_organization/04_Modules.md
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@@ -197,7 +197,7 @@ make sure you are running Python in a proper environment. Modules
are usually when programmers encounter problems with the current working are usually when programmers encounter problems with the current working
directory or with Python's path settings. directory or with Python's path settings.
### (a) Module imports ### Exercise 3.11: Module imports
In section 3, we created a general purpose function `parse_csv()` for parsing the contents of CSV datafiles. In section 3, we created a general purpose function `parse_csv()` for parsing the contents of CSV datafiles.
@@ -268,7 +268,7 @@ Try importing a function so that you don’t need to include the module name:
>>> >>>
``` ```
### (b) Using your library module ### Exercise 3.12: Using your library module
In section 2, you wrote a program `report.py` that produced a stock report like this: In section 2, you wrote a program `report.py` that produced a stock report like this:
@@ -292,7 +292,7 @@ and `read_prices()` functions to use the `parse_csv()` function.
Use the interactive example at the start of this exercise as a guide. Use the interactive example at the start of this exercise as a guide.
Afterwards, you should get exactly the same output as before. Afterwards, you should get exactly the same output as before.
### (c) Using more library imports ### Exercise 3.14: Using more library imports
In section 1, you wrote a program `pcost.py` that read a portfolio and computed its cost. In section 1, you wrote a program `pcost.py` that read a portfolio and computed its cost.
@@ -314,4 +314,4 @@ also contains `read_portfolio()` and `read_prices()` functions. And
finally, `pcost.py` which computes the portfolio cost, but makes use finally, `pcost.py` which computes the portfolio cost, but makes use
of the code written for the `report.py` program. of the code written for the `report.py` program.
[Next](05_Main_module) [Contents](../Contents) \| [Previous (3.3 Error Checking)](03_Error_checking) \| [Next (3.5 Main Module)](05_Main_module)

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Notes/03_Program_organization/05_Main_module.md
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@@ -249,7 +249,7 @@ if __name__ == '__main__':
## Exercises ## Exercises
### (a) `main()` functions ### Exercise 3.15: `main()` functions
In the file `report.py` add a `main()` function that accepts a list of command line options and produces the same output as before. In the file `report.py` add a `main()` function that accepts a list of command line options and produces the same output as before.
You should be able to run it interatively like this: You should be able to run it interatively like this:
@@ -278,7 +278,7 @@ Total cost: 44671.15
>>> >>>
``` ```
### (b) Making Scripts ### Exercise 3.16: Making Scripts
Modify the `report.py` and `pcost.py` programs so that they can execute as a script on the command line: Modify the `report.py` and `pcost.py` programs so that they can execute as a script on the command line:
@@ -297,3 +297,5 @@ bash $ python3 report.py Data/portfolio.csv Data/prices.csv
bash $ python3 pcost.py Data/portfolio.csv bash $ python3 pcost.py Data/portfolio.csv
Total cost: 44671.15 Total cost: 44671.15
``` ```
[Contents](../Contents) \| [Previous (3.4 Modules)](04_Modules) \| [Next (3.6 Design Discussion)](06_Design_discussion)

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Notes/03_Program_organization/06_Design_discussion.md
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@@ -85,7 +85,7 @@ Don't restrict your options. With great flexibility comes great power.
## Exercise ## Exercise
### (a)From filenames to file-like objects ### Exercise 3.17: From filenames to file-like objects
In this section, you worked on a file `fileparse.py` that contained a In this section, you worked on a file `fileparse.py` that contained a
function `parse_csv()`. The function worked like this: function `parse_csv()`. The function worked like this:
@@ -123,10 +123,12 @@ In this new code, what happens if you pass a filename as before?
With flexibility comes power and with power comes responsibility. Sometimes you'll With flexibility comes power and with power comes responsibility. Sometimes you'll
need to be careful. need to be careful.
### (b) Fixing existing functions ### Exercise 3.18: Fixing existing functions
Fix the `read_portfolio()` and `read_prices()` functions in the Fix the `read_portfolio()` and `read_prices()` functions in the
`report.py` file so that they work with the modified version of `report.py` file so that they work with the modified version of
`parse_csv()`. This should only involve a minor modification. `parse_csv()`. This should only involve a minor modification.
Afterwards, your `report.py` and `pcost.py` programs should work Afterwards, your `report.py` and `pcost.py` programs should work
the same way they always did. the same way they always did.
[Contents](../Contents) \| [Previous (3.5 Main module)](05_Main_module) \| [Next (4 Classes)](../04_Classes_objects/00_Overview)