def compose(self, function):
"""Creates a Function as composition of ``function`` with ``self``.
Function composition:
>>> f = Function(lambda a: -a).compose(abs)
>>> f(-1)
-1
Function composition operator ``**``:
>>> f = Function(lambda a: -a) ** abs
>>> f(-1)
-1
``**`` works on either side, no need to wrap both sides:
>>> f = Function(list) ** map << 1 .__add__
>>> f(range(10))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> f = list ** Function(map) << 1 .__add__
>>> f(range(10))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
"""
return self.clone(compose(self.invoke, self.clone(function)))
def compose(self, function):
"""Creates a Function as composition of ``function`` with ``self``.
Function composition:
>>> f = Function(lambda a: -a).compose(abs)
>>> f(-1)
-1
Function composition operator ``**``:
>>> f = Function(lambda a: -a) ** abs
>>> f(-1)
-1
``**`` works on either side, no need to wrap both sides:
>>> f = Function(list) ** map << 1 .__add__
>>> f(range(10))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> f = list ** Function(map) << 1 .__add__
>>> f(range(10))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
"""
return self.clone(compose(self.invoke, self.clone(function)))
def pipe(self, function):
"""Creates a Function that pipes output into ``function`` if invoked.
Piping output:
>>> f = Function(range).pipe(sum).pipe(int.__neg__)
>>> f(1, 101)
-5050
Pipe operator ``|``:
>>> f = Function(range) | sum | int.__neg__
>>> f(1, 101)
-5050
>>> f = Function(map) << 1 .__add__ | list
>>> f(range(10))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> sum_upto = 1 .__add__ | Function(range) << 1 | sum
>>> sum_upto(100)
5050
"""
return self.clone(compose(function, self.invoke))
def pipe(self, function):
"""Creates a Function that pipes output into ``function`` if invoked.
Piping output:
>>> f = Function(range).pipe(sum).pipe(int.__neg__)
>>> f(1, 101)
-5050
Pipe operator ``|``:
>>> f = Function(range) | sum | int.__neg__
>>> f(1, 101)
-5050
>>> f = Function(map) << 1 .__add__ | list
>>> f(range(10))
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> sum_upto = 1 .__add__ | Function(range) << 1 | sum
>>> sum_upto(100)
5050
"""
return self.clone(compose(function, self.invoke))
def test_compose():
identity = lambda a: a
# Left identity
f = int
g = compose(identity, f)
assert f('42') == g('42')
for n in range(42): # this number is not significant here.
assert f(n) == g(n)
# Right identity
f = str
g = compose(f, identity)
assert f(42) == g(42)
for n in range(42): # this number is not significant here.
assert f(n) == g(n)
# Associative
# NOTE: these functions are specifically chosen, so that when composed in
# different orders, yield different outputs.
f = hash
g = str
h = type
f1 = compose(f, compose(g, h))
f2 = compose(compose(f, g), h)
ns = [42, 0.5, '42', sum, f, lambda: 0]
for n in ns:
# make sure these functions yield different outputs when composed in
# different order,
assert f1(n) != compose(f, compose(h, g))(n)
assert f2(n) != compose(f, compose(h, g))(n)
assert f1(n) != compose(g, compose(f, h))(n)
assert f2(n) != compose(g, compose(f, h))(n)
assert f1(n) != compose(g, compose(h, f))(n)
assert f2(n) != compose(g, compose(h, f))(n)
assert f1(n) != compose(h, compose(g, f))(n)
assert f2(n) != compose(h, compose(g, f))(n)
assert f1(n) != compose(h, compose(f, g))(n)
assert f2(n) != compose(h, compose(f, g))(n)
# but compose should obey associative law.
assert f1(n) == f2(n)