Builtin Functions

Zip Function

• Takes iterables (lists, dictionaries, tuples, strings, etc) and zips them into tuples

• used for parallel iteration

• Return a zip object, which is an iterator of tuples

countries = ["America", "Australia", "England"]
cities = ["New York", "Sydney", "London"]
countries_and_cities = zip(countries,capitals)

countries_and_capitals.__next__() # can only call once, if need it more than one, need to reinitialize

• Zip will base on shortest iterables, to change it to base on longest one, use zip_longest

from itertools import zip_longest

countries = ["America", "Australia", "England", "France"]
cities = ["New York", "Sydney", "London"]
countries_and_cities = zip_longest(countries,capitals) # value will be None
countries_and_cities = zip_longest(countries,capitals, fillvalue="Fill when None")

Enumerate Function

• Add a counter to an iterable and returns it as an enumerate object

• The enumerate object is usually used in for loops

fruits = ["apple", "pineapple", "lemon", "watermelon", "grapes"]
enumerated_fruits = enumerate(fruits)
print(list(enumerated_fruits))
[(0, 'apple'), (1, 'pineapple'), (2, 'lemon'), (3, 'watermelon'), (4, 'grapes')]

enumerated_ted_fr = enumerate(fruits, start=5)
print(list(enumerated_fruits))
[(5, 'apple'), (6, 'pineapple'), (7, 'lemon'), (8, 'watermelon'), (9, 'grapes')]

for index, element in enumerate(fruits):
    print(index, element)
0 apple
1 pineapple
2 lemon
3 watermelon
4 grapes

Lambda Function

• Also called anonymous functions because they are unnamed

• Syntax: lambda arguments: expression

• can take any number of parameters

add = lambda x: x+5
print(add(7))
12

multiplication = lambda a,b,c: a*b*c
multiplication(4,5,2)
40

Sort and Sorted Function

• sort method only works for list

• sorted function works for any iterable

• If number is store as string it, sort will not sort it numerically

  • use $list.sort(key=int)

  • or $list.append(int(input)) to change individual item to integer

fruits = ["apple", "pineapple", "grapes", "watermelon"]
fruits.sort()
fruits
['apple', 'grapes', 'pineapple', 'watermelon']
fruits.sort(reverse=True)
fruits
['watermelon', 'pineapple', 'grapes', 'apple']


fruits = ["apple", "pineapple", "grapes", "watermelon"]
sorted(fruits)
['apple', 'grapes', 'pineapple', 'watermelon']
 sorted(fruits, reverse=True)
['watermelon', 'pineapple', 'grapes', 'apple']

fruits = {"apple":40 , "pineapple": 50, "grapes": 10, "watermelon":20}
sorted(fruits)
['apple', 'grapes', 'pineapple', 'watermelon']
def get_quantity(fruit):
    return fruits[fruit]
sorted(fruits, key=get_quantity) # sorted by quantity
['grapes', 'watermelon', 'apple', 'pineapple']

sorted(fruits, key=lambda fruit: fruits[fruit]) #using lambda instead of normal function
['grapes', 'watermelon', 'apple', 'pineapple']

Map function

• Applies a given function to each item of an iterable

• Returns a map object (which is an iterator)

• Shouuld be used instead of loop when possible

fruits = ["apple", "pineapple", "grapes", "watermelon"]
result=list()
for fruit in fruits:
    result.append(fruit.capitalize())
print(result)
['Apple', 'Pineapple', 'Grapes', 'Watermelon']

fruits = ["apple", "pineapple", "grapes", "watermelon"]
result = map(lambda fruit: fruit.capitalize(), fruits)
print(result)
<map object at 0x102d06580>
result.__next__() # can only iterate once
Apple
print(list(result))
['Apple', 'Pineapple', 'grapes', 'Watermelon']

fruits = ["apple", "pineapple", "grapes", "watermelon"]
def process(fruit):
    result_string = fruit.capitalize()
    if result_string.endswith("s"):
        result_string += " are great"
    else:
        result_string += " is great"
    return result_string
result = map(process,fruits)
print(list(result))
['Apple is great', 'Pineapple is great', 'Grapes are great', 'Watermelon is great']

Filter Function

• Contructs an iterator from elements of an iterable for which a function return True. In other words, it filters an iterable based on a condition given by a function

fruits = ["apple", "avocado", "watermelon", "grapes"]
filtered_fruits = filter(lambda fruit: fruit.startswith("a") == True, fruits)
filtered_fruits
filtered_fruits
<filter object at 0x1023ae580>
filtered_fruits.__next__()
'apple'
filtered_fruits.__next__()
'avocado'
filtered_fruits.__next__()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

filtered_fruits = filter(lambda fruit: fruit.startswith("a") == True, fruits)
>>> list(filtered_fruits)     
['apple', 'avocado']

fruits = {"apple": 60, "avocado": 40, "watermelon": 15, "grapes": 200}
filtered_fruits = filter(lambda t: t[1] > 50, fruits.items())
print(list(filtered_fruits))
[('apple', 60), ('grapes', 200)]

Any and All Function

Any

• Return True if any of the elements of the iterable is True and False otherwise

• At least one value is True -> True

• All values are False -> False

• Empty iterable -> False

fruits = ["apple", "pineapple", "watermelon", "avocado"]
fruits_mapped = map(lambda fruit: fruit.startswith("a"), fruits)
print(list(fruits_mapped))
[True, False, False, True]

any(fruits_mapped)
True

fruits_mapped = map(lambda fruit: len(fruit) > 50, fruits)
any(fruits_mapped)
False

All

• Return True if all elements of the iterable is True and False otherwise

• At least one value is False -> False

• All values are True -> True

• Empty iterable -> True

fruits = ["apple", "pineapple", "watermelon", "avocado"]
fruits_mapped = map(lambda fruit: len(fruit) < 50, fruits)
all(fruits_mapped)
True

Iterators

• An iterable is a representation of a series of elements that can be iterated over. It does not have any state such as a "current element". But every iterable can be converted to an iterator by using iter()

• An iterator is the object with iteration state. It can be checked to see if there're more elements using the next() or next() and move to the next element

fruits=["apple","watermelon","grapes"]
>>> next(fruits)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'list' object is not an iterator
>>> fruits.__next__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'list' object has no attribute '__next__'
 fruits=iter(fruits)
>>> next(fruits)
'apple'
>>> fruits.__next__()
'watermelon'