f-strings(Python 3.6) style literal string interpolation.

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Using f-strings(PEP 498) <https://www.python.org/dev/peps/pep-0498/>_ style literal string interpolation without Python 3.6.

Usages

Accessing the globals and locals.

.. code:: python

  import os
  import fmt as f

  g_foo = 'global-foo'
  g_bar = 'global-bar'
  g_num = 23
  g_ls = [1, 2, 3]

  def scope():
      l_foo = 'local-foo'
      l_bar = 'local-bar'
      print( f('{l_foo}, {l_bar}') )    # 'local-foo, local-bar'
      print( f('{g_foo}, {g_bar!r}') )  # "global-foo, 'global-bar'"

  scope()
  print( f('{{ }}') )                   # '{ }'
  print( f('hex: {g_num:#x}') )         # '0x17'
  print( f('{os.EX_OK}') )              # '0'
  print( f('{g_ls[0]}, {g_ls[1]}, {g_ls[2]}') )  # '1, 2, 3'

NOTE: Closure will be a little tricky, must pass the outside scope variables as arguments to f, which added a reference to inside the closure in order this can work.

.. code:: python

  import fmt as f

  def outer(x='xx'):
      y = 'yy'
      def inner():
          print( f('{x}, {y}', x, y) )  # "xx, yy"
      return inner

  outer()()

Expression evaluation.

.. code:: python

  from datetime import datetime
  import fmt as f

  class S(object):
      def __str__(self):
          return 'hello'
      def __repr__(self):
          return 'hi'
      def __format__(self, fmt):
          return 'abcdefg'[int(fmt)]

  print( f('{1234567890:,}') )             # '1,234,567,890'
  print( f('{1 + 2}') )                    # '3'
  print( f('{str(1 + 2)!r}') )             # "'3'"
  print( f('{[i for i in range(5)]}') )    # '[0, 1, 2, 3, 4]'
  ls = range(5)
  print( f('{{i for i in ls}}') )          # 'set([0, 1, 2, 3, 4])' or '{0, 1, 2, 3, 4}'
  print( f('{{k:v for k,v in zip(range(3), range(3, 6))}}') )  # '{0: 3, 1: 4, 2: 5}'
  print( f('{datetime(1994, 11, 6):%Y-%m-%d}') )               # '1994-11-06'
  print( f('{list(map(lambda x: x+1, range(3)))}') )           # '[1, 2, 3]'
  print( f('{S()!s}, {S()!r}, {S():1}') )                      # 'hello, hi, b'

Also, you can register some namespaces for convenience.

.. code:: python

  import fmt as f

  f.mregister({'x': 1, 'y': 2})  # register multiple
  f.register('z', 3)             # register only one

  def func(x, y):
      return x + y

  print( f('{func(x, y)}') )  # '3'
  print( f('{func(x, z)}') )  # '4'
  print( f('{func(y, z)}') )  # '5'