- Keyword args (**kwargs)
def f(x=1, y=2): return (x,y)
print(f()) # (1, 2)
print(f(3)) # (3, 2)
print(f(y=3)) # (1, 3) [here is where we use a keyword arg]
def f(x, **kwargs): return (x, kwargs)
print(f(1)) # (1, { })
print(f(2, y=3, z=4)) # (2, {'z': 4, 'y': 3})
- Functions inside functions
def f(L):
def squared(x): return x**2
return [squared(x) for x in L]
print(f(range(5)))
try:
print(squared(5))
except:
print("squared is not defined outside f")
- Closures + Non-local variables
def f(L):
myMap = dict()
def squared(x):
result = x**2
myMap[x] = result
return result
squaredList = [squared(x) for x in L]
return myMap
print(f(range(5)))
- Non-local variables fail on setting (use nonlocal)
def brokenF(L):
lastX = 0
def squared(x):
result = x**2
lastX = x
return result
squaredList = [squared(x) for x in L]
return lastX
print(brokenF(range(5)))
def fixedF(L):
lastX = 0
def squared(x):
nonlocal lastX
result = x**2
lastX = x
return result
squaredList = [squared(x) for x in L]
return lastX
print(fixedF(range(5)))
- Functions that return functions
def derivativeFn(f):
def g(x):
h = 10**-5
return (f(x+h) - f(x))/h
return g
def f(x): return 5*x**3 + 10
fprime1 = derivativeFn(f)
fprime2 = derivativeFn(fprime1)
print(f(3)) # 145, 5*x**3 + 10 evaluated at x == 3
print(fprime1(3)) # about 135, 15*x**2 evaluated at x == 3
print(fprime2(3)) # about 90, 30*x evaluated at x == 3
- Function decorators
@derivativeFn
def h(x): return 5*x**3 + 10
print(h(3)) # 135, matches fprime1 from above.