Functions


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# Use "def" to create new functions
def add(x, y):
    print("x is %s and y is %s" % (x, y))
    return x + y    # Return values with a return statement

# Calling functions with parameters
add(5, 6) #=> prints out "x is 5 and y is 6" and returns 11

# Another way to call functions is with keyword arguments
add(y=6, x=5)   # Keyword arguments can arrive in any order.

# You can define functions that take a variable number of positional arguments
def varargs(*args):
    return args

varargs(1, 2, 3) #=> (1,2,3)


# You can also define functions that take a variable number of keyword arguments
def keyword_args(**kwargs):
    return kwargs

# Let's call it to see what happens
keyword_args(big="foot", loch="ness") #=> {"big": "foot", "loch": "ness"}

# You can do both at once, if you like
def all_the_args(*args, **kwargs):
    print(args)
    print(kwargs)
"""
all_the_args(1, 2, a=3, b=4) prints:
    (1, 2)
    {"a": 3, "b": 4}
"""

# When calling functions, you can do the opposite of args/kwargs!
# Use * to expand tuples and use ** to expand kwargs.
args = (1, 2, 3, 4)
kwargs = {"a": 3, "b": 4}
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)

Advanced Functional Stuff


# Python has first class functions (Like Javascript)
def create_adder(x):
    def adder(y):
        return x + y
    return adder

add_10 = create_adder(10)
add_10(3) #=> 13

# There are also anonymous functions
(lambda x: x > 2)(3) #=> True

# There are built-in higher order functions
map(add_10, [1,2,3]) #=> [11, 12, 13]
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) #=> [6, 7]

# We can use list comprehensions for nice maps and filters
[add_10(i) for i in [1, 2, 3]]  #=> [11, 12, 13]
[x for x in [3, 4, 5, 6, 7] if x > 5] #=> [6, 7]

Challenge

The following function sums the even numbers of its parameters:

def sumEven(*vars):
    sum = 0
    for n in vars:
        if n%2==0:
            sum += n 
    return sum

For example, sumEven(2,3,4) would return 6.

You have a tuple named tup. Write one line of code (13 characters) that passes tup to sumEven() so it returns the sum of it's even numbers.

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Challenge

The function makeMultiplier, takes in one parameter, x. Fill in the function body so it returns a function that takes in one parameter y and returns the product of x and y.

For example, calling makeMultiplier(3) should return a function that returns 3*y, while calling makeMultiplierr(10) should return a function that returns 10*y.

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