Files

Files are named locations on the computer’s disk that permanently store information for future use of its data. They are used to permanently store data in non-volatile memory (e.g. hard disk) as opposed to volatile sources like Random Access Memory RAM, which loses its data when the computer is turned off.

File Handling

Handling files is a common feature that many languages use to work with the computer’s file system. In Python, file handling is possible and usually takes place in the following order:

1. Open (or create) the file.
2. Perform operations on the file, such as reading or writing to it.
3. Close the file to free up any resources used.

Example

The small example below demonstrates how one process of file handling could work:

# Create, or overwrite, a file and open for writing
file = open("myfile.txt", "w")
file.write("Hello world!")
file.close()

# Open existing file to read and print text content
file = open("myfile.txt", "r")
first_two_bytes = file.read(2)
next_three_bytes = file.read(3)
the_rest = file.read()
print(first_two_bytes, next_three_bytes, the_rest, sep="\n")
file.close()

In the first part of the code example, a plain text file named myfile.txt was created and opened in the "w" “write”-mode. Then a piece of text was written to the file and closed afterward.

In the next part, a few calls to the .read() method are assigned to some variables and then each one is printed on a new line:

He
llo
 world!

Files and the Command Line

Python files can be run as command line arguments using their filename.

python example_file.py

# Alternate
python3 example_file.py

This executes a file’s inner __main__ environment variable, which then runs the code within. This code may include variable declarations, operations, and function calls.

More on __main__

Any time a .py file is run and interpreted, certain variables are set up and linked with the file. This includes __main__ environment variable, which is assigned as the file’s __name__ variable. All Python programs feature these variables, which can be verified as in the following example:

# example.py

import imported_example

if __name__ == '__main__':
  print('Example file: ' + __name__)

print('Imported example file: ' + imported_example.__name__)

When python example.py is run on the command line, the following will be printed:

Example file: __main__
Imported example file: imported_example_file

The main file being run, example.py, has its __name__ set to __main__ while the imported_example.py file’s __name__ is literally set to the name of the file.

More information about file methods in Python can be found below.