reading-and-writing-files.md

title	description
Reading and writing files - Python Cheatsheet	To read/write to a file in Python, you will want to use the with statement, which will close the file for you after you are done, managing the available resources for you.

Reading and Writing Files

The file Reading/Writing process

To read/write to a file in Python, you will want to use the with statement, which will close the file for you after you are done, managing the available resources for you.

Opening and reading files with the open() function

>>> with open('C:\\Users\\your_home_folder\\hi.txt') as hello_file:
...     hello_content = hello_file.read()
...
>>> hello_content
'Hello World!'

Alternatively, you can use the readlines() method to get a list of string values from the file, one string for each line of text:

>>> with open('sonnet29.txt') as sonnet_file:
...     sonnet_file.readlines()
...
# [When, in disgrace with fortune and men's eyes,\n',
# ' I all alone beweep my  outcast state,\n',
# And trouble deaf heaven with my bootless cries,\n', And
# look upon myself and curse my fate,']

You can also iterate through the file line by line:

>>> with open('sonnet29.txt') as sonnet_file:
...     for line in sonnet_file:
...         print(line, end='')
...
# When, in disgrace with fortune and men's eyes,
# I all alone beweep my outcast state,
# And trouble deaf heaven with my bootless cries,
# And look upon myself and curse my fate,

Writing to files

>>> with open('bacon.txt', 'w') as bacon_file:
...     bacon_file.write('Hello world!\n')
...
# 13

>>> with open('bacon.txt', 'a') as bacon_file:
...     bacon_file.write('Bacon is not a vegetable.')
...
# 25

>>> with open('bacon.txt') as bacon_file:
...     content = bacon_file.read()
...
>>> print(content)
# Hello world!
# Bacon is not a vegetable.

Saving variables with the shelve module

To save variables:

>>> import shelve

>>> cats = ['Zophie', 'Pooka', 'Simon']
>>> with shelve.open('mydata') as shelf_file:
...     shelf_file['cats'] = cats

To open and read variables:

>>> with shelve.open('mydata') as shelf_file:
...     print(type(shelf_file))
...     print(shelf_file['cats'])
...
# <class 'shelve.DbfilenameShelf'>
# ['Zophie', 'Pooka', 'Simon']

Just like dictionaries, shelf values have keys() and values() methods that will return list-like values of the keys and values in the shelf. Since these methods return list-like values instead of true lists, you should pass them to the list() function to get them in list form.

>>> with shelve.open('mydata') as shelf_file:
...     print(list(shelf_file.keys()))
...     print(list(shelf_file.values()))
...
# ['cats']
# [['Zophie', 'Pooka', 'Simon']]

Reading ZIP files

>>> import zipfile, os

>>> os.chdir('C:\\')    # move to the folder with example.zip
>>> with zipfile.ZipFile('example.zip') as example_zip:
...     print(example_zip.namelist())
...     spam_info = example_zip.getinfo('spam.txt')
...     print(spam_info.file_size)
...     print(spam_info.compress_size)
...     print('Compressed file is %sx smaller!' % (round(spam_info.file_size / spam_info.compress_size, 2)))
...
# ['spam.txt', 'cats/', 'cats/catnames.txt', 'cats/zophie.jpg']
# 13908
# 3828
# 'Compressed file is 3.63x smaller!'

Extracting from ZIP Files

The extractall() method for ZipFile objects extracts all the files and folders from a ZIP file into the current working directory.

>>> import zipfile, os

>>> os.chdir('C:\\')    # move to the folder with example.zip

>>> with zipfile.ZipFile('example.zip') as example_zip:
...     example_zip.extractall()

The extract() method for ZipFile objects will extract a single file from the ZIP file:

>>> with zipfile.ZipFile('example.zip') as example_zip:
...     print(example_zip.extract('spam.txt'))
...     print(example_zip.extract('spam.txt', 'C:\\some\\new\\folders'))
...
# 'C:\\spam.txt'
# 'C:\\some\\new\\folders\\spam.txt'

Creating and Adding to ZIP Files

>>> import zipfile

>>> with zipfile.ZipFile('new.zip', 'w') as new_zip:
...     new_zip.write('spam.txt', compress_type=zipfile.ZIP_DEFLATED)

This code will create a new ZIP file named new.zip that has the compressed contents of spam.txt.