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David Beazley
2020-05-26 11:40:09 -05:00
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Notes/01_Introduction/06_Files.md
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# 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: