Python file handling - reading

Go to the [[Python Week 4 Main Page]] or the [[Python - Main Page]] Also see the [[Programming Main Page]] or the [[Main AI Page]]

For code examples see [[Week4 Reading From Files Lab]]

See [[Python file handling - writing]]

The 'open()' function

Syntax:

File1 = open("/home/websinthe/Documents/code/example.txt", "r")

• File1 <-- File object
• open <-- function name
• "/home/websinthe/.../example.txt" <-- file path
• "r" <-- mode

Common modes include:

• w <-- write (writes from beginning of file)
• r <-- read
• a <-- append
• r+ <-- read/write (need to take care of line cursor placement)
• x <-- create file

You use the file object to gain information about the file. Think of it as pouring the contents of the file into a variable and using the variable's methods to interact with the file's data.

File1.name --> /home/websinthe/Documents/code/example.txt File1.mode --> r File1.close --> you always need to close the file, which is why you always use the with statement instead of just opening a file straight up.

The 'with' context manager

#contextmanager

The with context manager ensures that the file being manipulated is closed after it is used without the code having to explicitly handle the file's closure.

with open("/home/websinthe/Documents/code/example.txt", "r") as File1:
	file_contents = File1.read()
	print(file_contents)

All operations within the indent block will be executed and then the file will be closed.

file_contents = File1.read() <-- outputs the contents of the file to the variable file_contents = File1.readlines() <-- outputs the lines of the file as elements of a list object to the variable file_contents = File1.readline() <-- outputs the first line of the file to the variable, ==each subsequent time it is called, it will output the next line to the variable== file_contents = File1.readlines(4) <-- outputs the first 4 characters of each line to the variable