# Use "def" to create new functions
def add(x, y):
print("x is {} and y is {}".format(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 define functions that take a variable number of
# keyword arguments, as well
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)
# Returning multiple values (with tuple assignments)
def swap(x, y):
return y, x # Return multiple values as a tuple without the parenthesis.
# (Note: parenthesis have been excluded but can be included)
x = 1
y = 2
x, y = swap(x, y) # => x = 2, y = 1
# (x, y) = swap(x,y) # Again parenthesis have been excluded but can be included.
# Function Scope
x = 5
def set_x(num):
# Local var x not the same as global variable x
x = num # => 43
print (x) # => 43
def set_global_x(num):
global x
print (x) # => 5
x = num # global var x is now set to 6
print (x) # => 6
set_x(43)
set_global_x(6)
# Python has first class functions
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
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
# There are built-in higher order functions
list(map(add_10, [1, 2, 3])) # => [11, 12, 13]
list(map(max, [1, 2, 3], [4, 2, 1])) # => [4, 2, 3]
list(filter(lambda x: x > 5, [3, 4, 5, 6, 7])) # => [6, 7]
# We can use list comprehensions for nice maps and filters
# List comprehension stores the output as a list which can itself be a nested list
[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]
# You can construct set and dict comprehensions as well.
{x for x in 'abcddeef' if x not in 'abc'} # => {'d', 'e', 'f'}
{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
Python *args and **kwargs
*args is the positional arguments in a function
and **kwargs is the keyword arguments in s function
def person(*args, **kwargs):
print('args (tuple):', args) # positional arguments
print('kwargs (dict):', kwargs) # keyword arguments
person('Football', 'Running', name='Alex', age=35)
# args (tuple): ('Football', 'Running')
# kwargs (dict): {'name': 'Alex', 'age': 35}
def person_2(hobby, *args, name, **kwargs):
print('hobby: ', hobby)
print('args (tuple):', args) # positional arguments
print('name: ', name)
print('kwargs (dict):', kwargs) # keyword arguments
person_2('Football', 'Running', 'Hockey', name='Alex', age=30, city='Ottawa')
# hobby: Football
# args (tuple): ('Running', 'Hockey')
# name: Alex
# kwargs (dict): {'age': 30, 'city': 'Ottawa'}
def person_3(*args, **kwargs):
print('args (tuple):', args) # positional arguments
print('kwargs (dict):', kwargs) # keyword arguments
args = ('Running', 'Hockey')
kwargs = {'name': 'Alex', 'age': 25}
person_3(*args, **kwargs)
# args (tuple): ('Running', 'Hockey')
# kwargs (dict): {'name': 'Alex', 'age': 25}