Coverage for sympy/core/rules.py : 47%

""" 

Replacement rules. 

""" 

from __future__ import print_function, division 

class Transform(object): 

""" 

Immutable mapping that can be used as a generic transformation rule. 

Parameters 

---------- 

transform : callable 

Computes the value corresponding to any key. 

filter : callable, optional 

If supplied, specifies which objects are in the mapping. 

Examples 

======== 

>>> from sympy.core.rules import Transform 

>>> from sympy.abc import x 

This Transform will return, as a value, one more than the key: 

>>> add1 = Transform(lambda x: x + 1) 

>>> add1[1] 

2 

>>> add1[x] 

x + 1 

By default, all values are considered to be in the dictionary. If a filter 

is supplied, only the objects for which it returns True are considered as 

being in the dictionary: 

>>> add1_odd = Transform(lambda x: x + 1, lambda x: x%2 == 1) 

>>> 2 in add1_odd 

False 

>>> add1_odd.get(2, 0) 

0 

>>> 3 in add1_odd 

True 

>>> add1_odd[3] 

4 

>>> add1_odd.get(3, 0) 

4 

""" 

def __init__(self, transform, filter=lambda x: True): 

self._transform = transform 

self._filter = filter 

def __contains__(self, item): 

return self._filter(item) 

def __getitem__(self, key): 

if self._filter(key): 

return self._transform(key) 

else: 

raise KeyError(key) 

def get(self, item, default=None): 

if item in self: 

return self[item] 

else: 

return default