- Variable length args (*args)
def longestWord(*args):
if (len(args) == 0): return None
result = args[0]
for word in args:
if (len(word) > len(result)):
result = word
return result
print(longestWord("this", "is", "really", "nice")) # really
mywords = ["this", "is", "really", "nice"]
print(longestWord(mywords)) # ['this', 'is', 'really', 'nice']
print(longestWord(*mywords)) # really
- Default args
- Default args example
def f(x, y=10): return (x,y)
print(f(5)) # (5, 10)
print(f(5,6)) # (5, 6)
- Do not use mutable default args
def f(x, L=[ ]):
L.append(x)
return L
print(f(1))
print(f(2)) # why is this [1, 2]?
- One workaround for mutable default args
def f(x, L=None):
if (L == None):
L = [ ]
L.append(x)
return L
print(f(1))
print(f(2)) # [2] (that's better)
- Functions as parameters
def derivative(f, x):
h = 10**-8
return (f(x+h) - f(x))/h
def f(x): return 4*x + 3
print(derivative(f, 2)) # about 4
def g(x): return 4*x**2 + 3
print(derivative(g, 2)) # about 16 (8*x at x==2)
- Lambda functions
print(derivative(lambda x:3*x**5 + 2, 2)) # about 240, 15*x**4 at x==2
myF = lambda x: 10*x + 42
print(myF(5)) # 92
print(derivative(myF, 5)) # about 10
- 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")
- 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.