Hướng dẫn python string too long

When using PEP8 code checkers such as flake8 in Python, an error, E501 line too long, is raised when one line exceeds 80 characters.

This article describes how to write a long string that does not contain a new line on multiple lines.

• Use a backslash [\] as a line continuation character
• Use parentheses

See the following article for various operations related to strings with line breaks.

• Handle line breaks [newlines] in Python

If you want to wrap or truncate long strings, the textwrap module is useful. See the following article.

• Wrap and truncate a string with textwrap in Python

If the number of characters in a line becomes too long due to method chaining, you can break the line in the same way.

• Method chains with line breaks in Python

Use a backslash [\] as a line continuation character

In Python, a backslash [\] is a line continuation character. If a backslash is placed at the end of a line, it is considered that the line is continued on the next line.

n = 1 + 2 \
    + 3

print[n]
# 6

Also, if multiple string literals are written sequentially, they are concatenated into one string as follows:

s = 'aaa' 'bbb'

print[s]
# aaabbb

Therefore, you can write a long string into multiple lines as follows:

s = '//ja.wikipedia.org/wiki/'\
    '%E3%83%97%E3%83%AD%E3%82%B0%E3%83'\
    '%A9%E3%83%9F%E3%83%B3%E3%82%B0%E8%A8%80%E8%AA%9E'

print[s]
# //ja.wikipedia.org/wiki/%E3%83%97%E3%83%AD%E3%82%B0%E3%83%A9%E3%83%9F%E3%83%B3%E3%82%B0%E8%A8%80%E8%AA%9E

Only string literals [string surrounded by ' or "] are concatenated if written consecutively. Note that in the case of variables, an error is raised.

s_var = 'xxx'

# s = 'aaa' s_var 'bbb'
# SyntaxError: invalid syntax

Use the + operator to concatenate variables, or variables and string literals.

s = 'aaa' + s_var + 'bbb'

print[s]
# aaaxxxbbb

You need the + operator to concatenate variables, even if they are separated by a backslash [\].

s = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'\
    + s_var\
    + 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb'

print[s]
# aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaxxxbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

See the following article for details of string concatenation.

• Concatenate strings in Python [+ operator, join, etc.]

Use parentheses

In Python, you can freely break the line in parentheses [[], {}, []]. Using this rule, you can write a long string on multiple lines with parentheses instead of backslashes.

Since {} is used for set and [] is used for list, use [] for such purpose. Note that tuple is created by commas, not [].

• A tuple with one element requires a comma in Python

You can write as follows.

s = ['//ja.wikipedia.org/wiki/'
     '%E3%83%97%E3%83%AD%E3%82%B0%E3%83'
     '%A9%E3%83%9F%E3%83%B3%E3%82%B0%E8%A8%80%E8%AA%9E']

print[s]
# //ja.wikipedia.org/wiki/%E3%83%97%E3%83%AD%E3%82%B0%E3%83%A9%E3%83%9F%E3%83%B3%E3%82%B0%E8%A8%80%E8%AA%9E

If variables are included, you need the + operator.

s = ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
     + s_var
     + 'bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb']

print[s]
# aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaxxxbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb