Recipe 1.14. Changing the Indentation of a Multiline String
Credit: Tom Good
Problem
You have a string made up of
multiple lines, and you need to build another string from it, adding
or removing leading spaces on each line so that the indentation of
each line is some absolute number of spaces.
Solution
The methods of string objects are quite handy, and let us write a
simple function to perform this task:def reindent(s, numSpaces):
leading_space = numSpaces * ' '
lines = [ leading_space + line.strip( )
for line in s.splitlines( ) ]
return '\n'.join(lines)
Discussion
When working with text, it may be necessary to change the indentation
level of a block. This recipe's code adds leading
spaces to or removes them from each line of a multiline string so
that the indentation level of each line matches some absolute number
of spaces. For example:>>> x = "" line one
... line two
... and line three
... ""
>>> print x
line one
line two
and line three
>>> print reindent(x, 4)
line one
line two
and line three Even if the lines in s are initially indented
differently, this recipe makes their indentation homogeneous, which
is sometimes what we want, and sometimes not. A frequent need is to
adjust the amount of leading spaces in each line, so that the
relative indentation of each line in the block is preserved. This is
not difficult for either positive or negative values of the
adjustment. However, negative values need a check to ensure that no
nonspace characters are snipped from the start of the lines. Thus, we
may as well split the functionality into two functions to perform the
transformations, plus one to measure the number of leading spaces of
each line and return the result as a list:def addSpaces(s, numAdd):
white = " "*numAdd
return white + white.join(s.splitlines(True))
def numSpaces(s):
return [len(line)-len(line.lstrip( )) for line in s.splitlines( )]
def delSpaces(s, numDel):
if numDel > min(numSpaces(s)):
raise ValueError, "removing more spaces than there are!"
return '\n'.join([ line[numDel:] for line in s.splitlines( ) ]) All of
these functions rely on the string method
splitlines, which is similar to a
split on '\n'.
splitlines has the extra ability to leave the
trailing newline on each line (when you call it with
true as its argument). Sometimes this turns out to
be handy: addSpaces could not be quite as short and
sweet without this ability of the splitlines
string method.Here's how we can combine these functions to build
another function to delete just enough leading spaces from each line
to ensure that the least-indented line of the block becomes flush
left, while preserving the relative indentation of the lines:def unIndentBlock(s):
return delSpaces(s, min(numSpaces(s)))
See Also
Library Reference and Python in a
Nutshell docs on sequence types. |
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