Python: Read Text File into List, Remove Newline

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Problem Formulation

Reading data from a text file into a list is a common operation in Python. It’s often necessary to remove newline characters from each line read from the file, as these can interfere with processing the data. We’ll explore several methods to read a file and remove newline characters in Python.

Method 1: Using strip()

The strip() method returns a new string after removing any leading and trailing whitespace characters, including newlines. Here is how you can use it:

with open('file.txt', 'r') as file:
    lines = [line.strip() for line in file]

This opens the file in reading mode, iterates over each line, strips the newline character using strip(), and collects the processed lines into a list.

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Method 2: Using rstrip()

The rstrip() method is used to remove trailing characters. By passing '\n' as an argument, it will remove any trailing newline characters from each line:

with open('file.txt', 'r') as file:
    lines = [line.rstrip('\n') for line in file]

This code also reads from the file and uses a list comprehension, but this time it calls rstrip('\n') on each line to remove only the trailing newline character.

Method 3: Using read().splitlines()

You can read the entire file content into a string and then split it into a list of lines without newlines using splitlines():

with open('file.txt', 'r') as file:
    lines = file.read().splitlines()

This approach first reads the whole file content into a single string and then applies splitlines(), which is a method that splits a string into a list at newline characters and does not include those newline characters in the result.

Method 4: Reading Binary and Decoding

If you’re dealing with a file with a specific encoding or need to handle various line endings (\r\n for Windows or \r for macOS), you can read the file in binary mode and decode it accordingly:

with open('file.txt', 'rb') as file:
    lines = file.read().decode('utf-8').splitlines()

This method reads the file content as a binary object, decodes it into a string using UTF-8 encoding (or any other encoding as required), and then splitlines() is applied to get a list of lines without newline characters.

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Summary/Discussion

The right method to remove newline characters when reading a file into a list depends on the presence of trailing whitespace or the need to handle different platforms’ newlines.

  • strip() is a good default choice because it also removes other trailing whitespaces, which is often desirable.
  • However, if you only want to remove newlines, rstrip('\n') is more explicit.
  • read().splitlines() is useful when handling large files, while reading in binary and decoding is suitable for ensuring correct encoding handling.

Work with context managers (with statement) to properly manage file I/O operations in Python.

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