files.md

Files

Reading files

To get a file for use in a script, use open(). A text file, somefile.txt, contains the following:

This is some text
Here is line two
And finally line three

some_file = open('somefile.txt') fetches the contents and stores in a variable.

read() and readlines() output the contents of the file into the console, starting at the beginning of the file and moving to the end. some_file.read() would return the entire content the first time, but nothing the second time as the position is at the end of the file. seek(0) resets position to 0 (the start of file).

Upon reading the file, Python will continue to have file open until close() is evoked. To get around this, the file can be opened as a variable:

with open('somefile.txt') as another_file:
    print(another_file.read())

* For more information on with, see context managers.

Read / write modes of open

mode='r' read only mode='w' write only (overwrites existing file or creates new one) mode='a' append only mode='r+' read and write mode='w+' write and read (overwrites existing file or creates new one)

For example, to append a line to an existing file:

with open('somefile.txt', mode='a') as another_file:
    another_file.write('\nThis is another line')

seek() is useful when appending to files. You can append content to a text file, for example, at the beginning by using seek(0) before appending.

Creating file with cell magic

%%writefile -a somefile.txt
One line
Another line

The above will do exactly as it imples: create a file in the pwd with the name somefile.txt with the two stated lines of content.

Cell magic are specific to IPyhon kernel. This works on Jupyter.