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How to Convert Multiline Strings to Single-Line Strings in Python

This guide explains how to convert multiline strings in Python into single-line strings. We'll cover removing extra whitespace, handling indentation, and choosing the best method for different scenarios.

Converting to a Single Line with splitlines() and join()​

The most common and versatile approach is to split the multiline string into lines, strip whitespace from each line, and then join the lines back together:

my_str = """\
First line
Second line
Third line
"""

result = " ".join(line.strip() for line in my_str.splitlines())
print(repr(result))  # Output: 'First line Second line Third line'
  • my_str.splitlines(): Splits the multiline string into a list of individual lines. Importantly, splitlines() handles different line endings (\n, \r, \r\n) correctly across different operating systems.
  • line.strip(): Removes leading and trailing whitespace from each line. This is crucial for removing extra spaces and newline characters.
  • " ".join(...): Joins the processed lines back into a single string, using a single space as the separator. You can use any separator you want here (e.g., "" for no separator, "," for a comma, etc.).
  • Generator Expression: The (line.strip() for line in ...) is a generator expression. It's memory-efficient, especially for very large strings, because it doesn't create an intermediate list.

Removing Leading/Trailing Whitespace and Empty Lines​

The previous example already handles extra spaces within lines. If you also want to remove completely empty lines (lines containing only whitespace), include an additional check:

import os # Needed for os.linesep

multiline_string = """\
First line

Second line

Third line


"""
# Using a generator expression and os.linesep for cross-platform compatibility
without_empty_lines = os.linesep.join([
    line for line in multiline_string.splitlines()
    if line.strip() != ''
])

print(without_empty_lines)

Output:

First line
Second line
Third line
  • if line.strip() != '': This condition checks if the line, after stripping whitespace, is not empty. Only non-empty lines are included in the result.
  • Using os.linesep ensures the correct line separator is used on all platforms (Windows, macOS, Linux). This is more robust than hardcoding \n.

Handling Indentation in Multiline Strings​

Multiline strings defined within Python code often have leading whitespace due to indentation.

Using textwrap.dedent()​

The textwrap.dedent() function removes any common leading whitespace from each line in a string:

from textwrap import dedent

multiline_str = """\
    first
    second
    third"""

print(dedent(multiline_str))

Output:

first
second
third
  • textwrap.dedent() removes the common leading whitespace, preserving relative indentation within the string. It doesn't remove all leading whitespace, only the common indent.

Using inspect.cleandoc()​

The inspect.cleandoc() function goes a step further than textwrap.dedent(): it also removes any empty lines at the beginning and end of the string:

from inspect import cleandoc

multiline_str = """

    first
    second
    third

"""
# Removes leading/trailing blank lines AND common indentation
print(cleandoc(multiline_str))

#Output:

first
second
third
  • inspect.cleandoc() is useful when you want to clean up multiline strings that might have extra blank lines due to how they're written in your code.

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