Is it possible to break a long line to multiple lines in Python? [duplicate]

This question already has answers here: How can I do a line break (line continuation) in Python? (10 answers)开发者_StackOverflow社区 Closed 4 years ago.

Just like C, you can break a long line into multiple short lines. But in Python, if I do this, there will be an indent error... Is it possible?

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From PEP 8 - Style Guide for Python Code:

The preferred way of wrapping long lines is by using Python's implied line continuation inside parentheses, brackets and braces. If necessary, you can add an extra pair of parentheses around an expression, but sometimes using a backslash looks better. Make sure to indent the continued line appropriately.

Example of implicit line continuation:

a = some_function(
    '1' + '2' + '3' - '4')

On the topic of line breaks around a binary operator, it goes on to say:

For decades the recommended style was to break after binary operators. But this can hurt readability in two ways: the operators tend to get scattered across different columns on the screen, and each operator is moved away from its operand and onto the previous line.

In Python code, it is permissible to break before or after a binary operator, as long as the convention is consistent locally. For new code Knuth's style (line breaks before the operator) is suggested.

Example of explicit line continuation:

a = '1'   \
    + '2' \
    + '3' \
    - '4'

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There is more than one way to do it.

1). A long statement:

>>> def print_something():
         print 'This is a really long line,', \
               'but we can make it across multiple lines.'

2). Using parenthesis:

>>> def print_something():
        print ('Wow, this also works?',
               'I never knew!')

3). Using \ again:

>>> x = 10
>>> if x == 10 or x > 0 or \
       x < 100:
       print 'True'

Quoting PEP8:

The preferred way of wrapping long lines is by using Python's implied line continuation inside parentheses, brackets and braces. If necessary, you can add an extra pair of parentheses around an expression, but sometimes using a backslash looks better. Make sure to indent the continued line appropriately. The preferred place to break around a binary operator is after the operator, not before it.

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If you want to assign a long string to variable, you can do it as below:

net_weights_pathname = (
    '/home/acgtyrant/BigDatas/'
    'model_configs/lenet_iter_10000.caffemodel')

Do not add any comma, or you will get a tuple which contains many strings!

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It works in Python too:

>>> 1+\
      2+\
3
6
>>> (1+
          2+
 3)
6

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When trying to enter continuous text (say, a query) do not put commas at the end of the line or you will get a list of strings instead of one long string:

queryText= "SELECT * FROM TABLE1 AS T1"\
"JOIN TABLE2 AS T2 ON T1.SOMETHING = T2.SOMETHING"\
"JOIN TABLE3 AS T3 ON T3.SOMETHING = T2.SOMETHING"\
"WHERE SOMETHING BETWEEN <WHATEVER> AND <WHATEVER ELSE>"\
"ORDER BY WHATEVERS DESC"

kinda like that.

There is a comment like this from acgtyrant, sorry, didn't see that. :/

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DB related code looks easier on the eyes in multiple lines, enclosed by a pair of triple quotes:

SQL = """SELECT
            id, 
            fld_1, 
            fld_2, 
            fld_3, 
            ...... 
         FROM some_tbl"""

than the following one giant long line:

SQL = "SELECT id, fld_1, fld_2, fld_3, .................................... FROM some_tbl"

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As far as I know, it can be done. Python has implicit line continuation (inside parentheses, brackets, and strings) for triple-quoted strings ("""like this""") and the indentation of continuation lines is not important. For more information, you may want to read this article on lexical analysis, from python.org.