fstring427
==========
Python 3.6 f-string sympathy (partial compatibility) module for Python
2.7 See https://www.python.org/dev/peps/pep-0498/ for the specification
for *Literal String Interpolation*.
Example from PEP-0498
---------------------
::
>>> import datetime
>>> name = 'Fred'
>>> age = 50
>>> anniversary = datetime.date(1991, 10, 12)
>>> f'My name is {name}, my age next year is {age+1}, my anniversary is {anniversary:%A, %B %d, %Y}.'
'My name is Fred, my age next year is 51, my anniversary is Saturday, October 12, 1991.'
>>> f'He said his name is {name!r}.'
"He said his name is 'Fred'."
Sympathetic output from fstring427
----------------------------------
::
>>> from fstring427.fstring import Fmt as f
>>> import datetime
>>> name = 'Fred'
>>> age = 50
>>> anniversary = datetime.date(1991,10,12)
>>> str(f('My name is {name}, my age next year is {age+1}, my anniversary is {anniversary:%A, %B %d, %Y}.'))
'My name is Fred, my age next year is 51, my anniversary is Saturday, October 12, 1991.'
>>> f('He said his name is {name!r}')()
"He said his name is 'Fred'"
Note the major differences:
- ``f`` is a class, not a string type
- ``f()`` evaluates the string
- str() of a instance of ``f`` also evaluates the string
The underlying implementation is a subclass of the Python 2.7 Format
class, and depends on internals. Obviously fragile and probably
non-portable, but still serves my purpose.
## ``printf()``, a convenience function
``>>> printf('He said his name is {name!r}') He said his name is 'Fred'``
which has the additional convenience of a temporary scope for kwargs
::
>>> printf('He said his name is {name!r}', name="Sam")
He said his name is 'Sam'
Major incompatibilities
-----------------------
Python 3.6 f-strings were carefully designed, and cover edge cases that
.format() does not, see
https://mail.python.org/pipermail/python-ideas/2015-July/034726.html
fstring427 was implemented on top of .format() and shares the underlying
implementation of lookups. If .format() can't handle a ``{field}``,
fstring427 will evaluate field as a Python expression in the proper
scope. In practice this means that:
::
a = 10
d = {'a': 'string', 10: 'int'}
printf("{d[a]")
prints ``string`` (Python 2.7 .format() behavior) instead of ``int``
(Python 3.6 f-string behavior). I've found this a small price to pay in
my 2.7 code to get cleaner printing and string formatting.
Roadmap
-------
- Add ``printf()`` style logging module
- Contemplate 2-3 port for printf() utility function (dealing with the
kwargs scope)
*Copyright 2017, Smartvid.io*
