How to write very long string that conforms with PEP8 and prevent E501

python

prompt-engineering

best-practices

f-strings

byNikita Barsukov·Oct 8, 2024

When handling long strings, Python allows you to split them into short segments enclosed in parentheses to implicitly join them — This way, it's both readable and PEP8 compliant:

long_string = (
    "This is the start of the tale, "
    "Continuing the narrative from the above, "
    "Concluding the epic saga of PEP8 compliance."
)

You can also employ backslashes for explicit line continuation, but implicit joining tends to be cleaner:

long_string = "It was a dark and stormy night, " \
              "The wind howled through the trees."

Hold that thought, there're more strategies to deal with long strings while adhering to PEP8!

String Concatenation: The No '+' Rule

It's recommended not to use the + operator for joining string literals in Python as it often results in less readable code:

# Not recommended
long_string = "First sentence, " + "second sentence, " + "third sentence."

# Recommended
long_string = (
    "First sentence, " 
    "second sentence, " 
    "third sentence." 
    # Yeah, you can keep it going...
)

The parenthesized strings, right besides each other, get concatenated implicitly and render line continuation superfluous.

Formatting With Spaces and Commas

If you have strings that need to be separated by commas and spaces, leave a comma and a blank space at the end of each line. This simple trick drastically improves the readability and editability:

shopping_list = (
    "Apples, " # An apple a day keeps the doctor away. 
    "Bananas, " # Keep calm and eat bananas.
    "Carrots." # Because, why not?
)

Parentheses: Boon and Bane

When using parentheses, avoid unwanted tuples. It's important to be vigilant:

# Creates a tuple, not a string!
not_string = ( 
    "Cats and ", 
    "Dogs!" # Help! I didn't mean to make a tuple!
)

# Joan below formats her string correctly
long_string = (
    "Hello StackOverflow, " 
    "I clearly am not a tuple!" 
)

Forgive my Length, E501

Occasionally, you might need to bypass PEP8 with a long line that serves a specific purpose. In these cases, you can disable E501 using # noqa: E501:

long_url = 'http://www.example.com/incredibly/long/url/address/that/gives/everyone/a/headache'  # noqa: E501

This is your "get out of jail free card" to avoid the error Code Police.

Using Fancy f-Strings

With f-strings, you can dynamically insert variables inside your long strings, all the while maintaining readability and complying with PEP8:

name = "Alice"
occupation = "Developer"
greetings = (
    f"Hello there, I am {name}, "  # Hi, Alice
    f"and I am a {occupation}."    # Cool job, Alice
)

Tipping The Scales: Readability vs Compliance

There are times when preserving readability might warrant breaching the 79-character rule as prescribed by PEP8. Certain information, like URLs or error messages, are more understandable when kept whole. Breathe easy, for autoscaling formatters like Black, take care of these cases.

explain-codes / Python / How to write very long string that conforms with PEP8 and prevent E501

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