How can I do a line break line continuation in Python

Question

I have a long line of code that I want to break up among multiple lines  What do I use and what is the syntax   For example  adding a bunch of strings   e    a     b     c     d    and have it in two lines like this   e    a     b         c     d

User · Answer

Taken from The Hitchhiker s Guide to Python  Line Continuation    When a logical line of code is longer than the accepted limit  you need to split it over multiple physical lines  The Python interpreter will join consecutive lines if the last character of the line is a backslash  This is helpful in some cases  but should usually be avoided because of its fragility  a white space added to the end of the line  after the backslash  will break the code and may have unexpected results  A better solution is to use parentheses around your elements  Left with an unclosed parenthesis on an end-of-line the Python interpreter will join the next line until the parentheses are closed  The same behaviour holds for curly and square braces  However  more often than not  having to split a long logical line is a sign that you are trying to do too many things at the same time  which may hinder readability   Having that said  here s an example considering multiple imports  when exceeding line limits  defined on PEP-8   also applied to strings in general  from app import       app  abort  make response  redirect  render template  request  session

User · Answer

Put a   at the end of your line or enclose the statement in parens         From IBM   b     i1  lt  20  and       i2  lt  30  and       i3  lt  40     or  b    i1  lt  20  and        i2  lt  30  and        i3  lt  40

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You can break lines in between parenthesises and braces  Additionally  you can append the backslash character   to a line to explicitly break it   x    tuples first value       second value  y   1         2

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What is the line   You can just have arguments on the next line without any problems  a   dostuff blahblah1  blahblah2  blahblah3  blahblah4  blahblah5               blahblah6  blahblah7   Otherwise you can do something like this  if  a    True and     b    False    or with explicit line break  if a    True and      b    False   Check the style guide for more information  Using parentheses  your example can be written over multiple lines  a     1     2     3         4     5    The same effect can be obtained using explicit line break  a    1     2     3           4     5   Note that the style guide says that using the implicit continuation with parentheses is preferred  but in this particular case just adding parentheses around your expression is probably the wrong way to go

User · Answer

It may not be the Pythonic way  but I generally use a list with the join function for writing a long string  like SQL queries   query       join        SELECT   FROM  TableName         WHERE  SomeColumn1  VALUE        ORDER BY  SomeColumn2         LIMIT 5

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If you want to break your line because of a long literal string  you can break that string into pieces  long string    quot a very long string quot  print  quot a very long string quot    will be replaced by long string        quot a  quot     quot very  quot     quot long  quot     quot string quot    print     quot a  quot     quot very  quot     quot long  quot     quot string quot     Output for both print statements  a very long string Notice the parenthesis in the affectation  Notice also that breaking literal strings into pieces allows to use the literal prefix only on parts of the string and mix the delimiters  s          2 2       f quot  2 2  quot

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One can also break the call of methods  obj method    in multiple lines  Enclose the command in parenthesis  quot    quot  and span multiple lines   gt  res    some object           apply args            filter             values   For instance  I find it useful on chain calling Pandas Holoviews objects methods

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From the horse s mouth  Explicit line   joining       Two or more physical lines may be   joined into logical lines using   backslash characters      as follows    when a physical line ends in a   backslash that is not part of a string   literal or comment  it is joined with   the following forming a single logical   line  deleting the backslash and the   following end-of-line character  For   example   if 1900  lt  year  lt  2100 and 1  lt   month  lt   12      and 1  lt   day  lt   31 and 0  lt   hour  lt  24      and 0  lt   minute  lt  60 and 0  lt   second  lt  60      Looks like a valid date         return 1       A line ending in a backslash cannot   carry a comment  A backslash does not   continue a comment  A backslash does   not continue a token except for string   literals  i e   tokens other than   string literals cannot be split across   physical lines using a backslash   A   backslash is illegal elsewhere on a   line outside a string literal

User · Answer

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  Long lines can be broken over multiple lines by wrapping expressions in parentheses  These should be used in preference to using a backslash for line continuation       Backslashes may still be appropriate at times  For example  long  multiple with-statements cannot use implicit continuation  so backslashes are acceptable   with open   path to some file you want to read   as file 1            open   path to some file being written    w   as file 2      file 2 write file 1 read          Another such case is with assert statements       Make sure to indent the continued line appropriately  The preferred place to break around a binary operator is after the operator  not before it  Some examples   class Rectangle Blob        def   init   self  width  height                   color  black   emphasis None  highlight 0           if  width    0 and height    0 and                 color     red  and emphasis     strong  or                 highlight  gt  100               raise ValueError  sorry  you lose           if width    0 and height    0 and  color     red  or                                            emphasis is None               raise ValueError  I don t think so -- values are  s   s                                  width  height           Blob   init   self  width  height                        color  emphasis  highlight     PEP8 now recommends the opposite convention  for breaking at binary operations  used by mathematicians and their publishers to improve readability   Donald Knuth s style of breaking before a binary operator aligns operators vertically  thus reducing the eye s workload when determining which items are added and subtracted   From PEP8  Should a line break before or after a binary operator       Donald Knuth explains the traditional rule in his Computers and Typesetting series   Although formulas within a paragraph always break after binary operations and relations  displayed formulas always break before binary operations  3        Following the tradition from mathematics usually results in more readable code     Yes  easy to match operators with operands income    gross wages             taxable interest              dividends - qualified dividends            - ira deduction           - student loan interest        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 is suggested     3   Donald Knuth s The TeXBook  pages 195 and 196

User · Answer

The danger in using a backslash to end a line is that if whitespace is added after the backslash  which  of course  is very hard to see   the backslash is no longer doing what you thought it was   See Python Idioms and Anti-Idioms  for Python 2 or Python 3  for more

[python] How can I do a line break (line continuation) in Python?

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