Python for loop to read file line by line
Jul 14, 2025 am 02:47 AM
Using for loop to read files line by line is an efficient way to process large files. 1. The basic usage is to open the file with open() and automatically manage the closing. Combined with for line in file to traverse each line, line.strip() can remove line breaks and spaces; 2. If you need to record the line number, you can use enumerate(file, start=1) to start the line number; 3. When processing non-ASCII files, you should specify encoding parameters such as utf-8 to avoid encoding errors. These methods are concise and practical, and are suitable for most text processing scenarios.
When you want to use Python to read file contents line by line, for loop is a very direct and efficient method. Compared to loading the entire file into memory at one time, reading line by line is more suitable for processing large files and saves resources.
The following common methods are the writing methods that are often used in actual development.
The most basic way to read for loops
The most commonly used method is this:
with open('example.txt', 'r') as file:
for line in file:
print(line.strip()) The advantage of this method is its simplicity and easy to read. You don't need to call read() or close() file manually, with statement will automatically help you handle these things.
-
'r'ofopen()means to open the file in read-only mode. - The
fileobject itself is an iterable object, and each iteration returns a row of content. -
line.strip()can remove line breaks and before and after spaces at the end of each line, and can also be replaced withrstrip('\n')as needed to just use line breaks.
If you just want to iterate through the file content and do simple processing on each line, such as finding keywords or statistics, this writing method is enough.
If you want to know which line is currently
Sometimes, not only reading content, but also want to record line numbers, you can use enumerate() :
with open('example.txt', 'r') as file:
for idx, line in enumerate(file, start=1):
print(f"Line {idx}: {line.strip()}") Here start=1 is to make the line number start from 1 instead of the default 0.
This method is very suitable for debugging or outputting logs, and can quickly locate the content of which line.
What to do if you encounter coding problems?
If you report an error when reading Chinese or other non-ASCII content, remember to add encoding parameters:
with open('example.txt', 'r', encoding='utf-8') as file:
for line in file:
print(line.strip()) In addition to utf-8 , common encodings also include gbk , latin-1 , etc., which depends on how your file is saved.
If you are not sure, you can try utf-8 first, and then try other things if you don't.
Basically that's it.
Reading files with for loop is not complicated, but there are several points that are easy to ignore, such as forgetting to use with causes the file to be closed, or failing to process newlines to affect subsequent judgments. Just pay attention to these details and you can process text files stably.
The above is the detailed content of Python for loop to read file line by line. For more information, please follow other related articles on the PHP Chinese website!
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