Python reading file one line at a time

Here is a working example of using for-loop to read line-by-line from a given file. The file that we are going to use here is test. The contents of test. Save the file test. You can make use of a while loop and read the contents from the given file line-by-line. To do that, first, open the file in read mode using open function.

The file handler returned from open , use it inside while —loop to read the lines. Python readline function is used inside while-loop to read the lines. In the case of for-loop, the loop terminates when the end of the file is encountered.

But the same is not the case with a while-loop, and you need to keep a check to see if the file is done reading. So once the readline function returns an empty string, you can make use of the break statement to terminate from the while —loop. The file that we are going to make use is test. Skip to content. What is Python readline? In this tutorial, we will see 3 examples of reading a text file in Python 3. How To Read all lines in a file at once?

Share this: Twitter Facebook. Related posts: How to read entire text file in Python? Go to mobile version. As you can see here , OP's program is correctly written. Hyperboreus: Well, his problem is that he's getting the whole file as the first line in a for line in file loop, and doesn't want to. A question about someone who wants to get the whole file by explicitly calling read instead of looping and has run into some weird bug that he worked around with mmap isn't likely to help him.

Show 3 more comments. Active Oldest Votes. In other words, just change one line: with open inStream, "rU" as f: Python 3 : Universal newlines are part of the standard behavior; adding "U" has no effect and is deprecated. Improve this answer. Seth 5, 5 5 gold badges 41 41 silver badges 54 54 bronze badges. AndreaMoro: I'm surprised that you'd have classic-Mac text files lying around.

I don't have any on my MacBook. I did recently find a Jaz disk which is probably full of source code for MacOS 6 programs, but I'm not sure how you'd get the files off such a thing nowadays… Anyway, glad it helped. I've created one file copy and pasting from some rows in Excel. Perhaps my fault? Or perhaps a problem with TextEdit that has been used for saving the file. Now, although much better, we don't even need to call the readlines method to achieve this same functionality.

This is the traditional way of reading a file line-by-line, but there's a more modern, shorter one. The returned File itself is an iterable. We don't need to extract the lines via readlines at all - we can iterate the returned object itself. This also makes it easy to enumerate it so we can write the line number in each print statement. This is the shortest, most Pythonic approach to solving the problem, and the approach favored by most:.

Here, we're taking advantage of the built-in functionalities of Python that allow us to effortlessly iterate over an iterable object, simply using a for loop. If you'd like to read more about Python's built-in functionalities on iterating objects, we've got you covered:. How can you use this practically? Most NLP applications deal with large corpora of data. Most of the time, it won't be wise to read the entire corpora into memory. While rudimentary, you can write a from-scratch solution to count the frequency of certain words, without using any external libraries.

Let's write a simple script that loads in a file, reads it line-by-line and counts the frequency of words, printing the 10 most frequent words and the number of their occurrences:.