How to Open a File in Python
Before the advent of databases, web services and other exotic forms of data storage, there was the file. Files will always be part of computing in one form or another. You can learn to use Python's file operations to open a file.
Open a File in Python
Determine the name of the file you wish to open. If the file does not already exist, you can create the file automatically with the file name you choose.
Determine whether you will be reading from the file, writing to the file or both.
Check to see if you have the correction permissions to read, write or create the file. You may need to check the permissions of the directory that the file exists in to make sure that you have read/write access. Under a Windows system, you can right click on the file or folder and check the attribute tab. Under a Unix or Mac OS X system, you can type:
percent ls -la myfile.txt
to check your permissions, and then
percent chmod 644 myfile.txt
to make sure you have permissions to write to the file.
Use the open() method to open a file and create a file object:
myfile = open("myfile.txt")
This will open or create myfile.txt for reading and for writing.
Know that if you wish to open a file only for reading or only for writing, you can pass a second argument to open(). Pass 'r' for read only, 'w' for write only and 'rw' for explicit read-write. For example:
#open a file for read only
myfile = open('myfile.txt', 'r')
Be sure to call the close() method to close any open file handles once you are done using the file, so that later processes can access the file:
Tips & Warnings
- For those who have used C and are transitioning to Python, the Python file operations are based upon C's stdio package. File operations that are called once the file is open will behave in a similar way to any language that is based upon stdio.
- The Python core documentation contains an extensive overview of all the options to open a file, as well as what operations you can perform once the file is open.
- If a file is open and locked by another process for writing, you may not be able to successfully open the file for writing in your Python process. If this is the case, an IOError exception will be raised.