Abstract

This PEP describes an interpretation of multiline string constants for Python. It suggests stripping spaces after newlines and stripping a newline if it is first character after an opening quotation.

Rationale

This PEP proposes an interpretation of multiline string constants in Python. Currently, the value of string constant is all the text between quotations, maybe with escape sequences substituted, e.g.:

def f():
    """
    la-la-la
    limona, banana
    """

def g():
    return "This is \
    string"

print repr(f.__doc__)
print repr(g())

prints:

'\n\tla-la-la\n\tlimona, banana\n\t'
'This is \tstring'

This PEP suggest two things:

• ignore the first character after opening quotation, if it is newline
• ignore in string constants all spaces and tabs up to first non-whitespace character, but no more than current indentation.

After applying this, previous program will print:

'la-la-la\nlimona, banana\n'
'This is string'

To get this result, previous programs could be rewritten for current Python as (note, this gives the same result with new strings meaning):

def f():
    """\
la-la-la
limona, banana
"""

def g():
  "This is \
string"

Or stripping can be done with library routines at runtime (as pydoc does), but this decreases program readability.

Implementation

I’ll say nothing about CPython, Jython or Python.NET.

In original Python, there is no info about the current indentation (in spaces) at compile time, so space and tab stripping should be done at parse time. Currently no flags can be passed to the parser in program text (like from __future__ import xxx). I suggest enabling or disabling of this feature at Python compile time depending of CPP flag Py_PARSE_MULTILINE_STRINGS.

Alternatives

New interpretation of string constants can be implemented with flags ‘i’ and ‘o’ to string constants, like:

i"""
SELECT * FROM car
WHERE model = 'i525'
""" is in new style,

o"""SELECT * FROM employee
WHERE birth < 1982
""" is in old style, and

"""
SELECT employee.name, car.name, car.price FROM employee, car
WHERE employee.salary * 36 > car.price
""" is in new style after Python-x.y.z and in old style otherwise.

Also this feature can be disabled if string is raw, i.e. if flag ‘r’ specified.

Copyright

This document has been placed in the Public Domain.