Notes: Opening, Reading and Closing Text Files

Sandbox Demo

Final Version

In Python, when you want to use a text file in your program you must ALWAYS perform the following tasks in order:

Open the file
Process the file (Read, Write, Append, etc.)
Close the file

Opening a File

For Python, “file” is the object that will provide basic functions and methods required to manipulate files. You need to use open() before you can read, append or write to a file.

The open() function will open a file and set the file pointer to the beginning of the file

GENERAL SYNTAX: fileObject = open(path/filename, mode)

The path/filename is the name of the file (with the path if the file is NOT in the same folder as the program) you want opened
The mode refers to how the file will be opened: “r” for reading, “w” for writing, “w+” for writing and reading and “a” for appending. The default is 'r'.

What happens if the file does not exist?

Reading from the File

Once the file is open, you can perform read actions on the file. In this lesson we will explore two of the read methods available to us.

read( ) will return the entire contents of the file as one big string and leave the file pointer at the end of the file
GENERAL SYNTAX: stringVariableName = fileObjectName.read( )
read(number) will return the number of characters indicated from the current position of the file pointer
GENERAL SYNTAX: stringVariableName = fileObjectName.read(15) - reads the next 15 characters
readline( ) will return the current line if the file pointer is at the beginning of the line and the remainder of the line if the pointer is somewhere else. The the file pointer is set at the beginning of the next line.
GENERAL SYNTAX: stringVariableName = fileObjectName.readline( ) - reads the current line and stores it in the variable.

Closing a File

Once you are done processing a file in your Python program you should always close it.

The close( ) method will close the file in Python.

GENERAL SYNTAX: fileObjectName.close( )