How to analyze a file line by line with Python

One of the main reasons people use Python is to analyze and manipulate text. If your program needs to process a file, it's usually best to read the file one line at a time to get an idea of ​​memory space and processing speed. This is best done with a while loop.

Code example for parsing text line by line

fileIN = open(sys.argv[1], "r")
line = fileIN.readline()
while line:
[some bit of analysis here]
line = fileIN.readline()

This code takes the first command line argument as the The name of the file. The first line opens it and starts a file object "fileIN". The second line then reads the first line of that file object and assigns it to the string variable "line". The while loop is executed based on the constancy of "line". When "line" changes, the cycle starts again. This will continue until no more file lines are read. The program then exits.

Reading the file this way, the program won't bite off more data than it's set up to handle. It processes the input data faster and provides the output step by step. In this way, the program's memory footprint is kept low and the computer's processing speed is not affected. If you are writing a CGI script you may see hundreds of instances of yourself running at a time, this is very important.

More about "While" in Python

The while loop statement will execute the target statement repeatedly as long as the condition is true.

The syntax of while loop in Python is:

while expression:
statement(s)

The statement can be a single statement or a series of statements. All statements indented by the same amount are considered part of the same code block. Indentation is Python's way of representing groups of statements.

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