text = "Hello World"

print(len(text))  # 11

print (text + " to every one.") # Hello World to every one.

print("H" in text, "hi" in text) # True False

for char in text:
    print(char, end=" ")    
# H e l l o   W o r l d

text = "hello world"

print(text[2]) # regular index: "l"
print(text[2:]) # from index 2 to end: "llo world"
print(text[0:3]) # first three: "hel"
print(text[::4]) # every fourth character: "hor"
print(text[3::2]) # from index 3, every other characters: "l ol"

hi = "Hi"
text = "hello world"

# find the index of the first occurrence of a substring, -1 if not found
print(text.find('o')) # 4
print(text.find("alice")) # -1

# Lower case, upper case and title case
print(hi.lower()) # hi
print(text.upper()) # HELLO WORLD
print(text.title()) # Hello World

# split a string into a list by the specified separator string
# default is white space
print(text.split()) # ["hello", "world"]
print(text.split("ll"))  # ["he", "o world"]

# replace a substr with another substr
print(hi.replace('i', 'a')) # Ha
print(text.replace("world", "alice")) # hello alice

# join a list of strings together with the desired separator string
print(", ".join(["alice", "bob", "cindy"])) # alice, bob, cindy

# create a list from literals
some_numbers = [3, 5 ,7]
names = ['Alice', 'Bob', 'Cindy']
# elements can be of different types - not recommended
some_data = [3, 'Alice', 12.5] 

# use list() function
generated_numbers = list(range(3, 8, 2))
letters = list('abc')

# print can print a list directly
print(generated_numbers)
print(letters)

numbers = [3, 5 ,7]

print(numbers[0], numbers[1], numbers[2])

print(numbers[-1], numbers[-2], numbers[-3])

# oops, IndexError if the index is out of range
print(numbers[5])

numbers = [1, 2, 3, 4, 5]
first, second, *rest = numbers
print(first, second, rest) # 1 2 [3, 4, 5]

first, _, third, *_ = numbers
print(first, third) # 1, 3

first, second, *_ = numbers
print(first, second) # 1, 2

first, *_, last = numbers
print(first, last) # 1, 5

numbers = list(range(3, 8, 2))

# use for
for number in numbers:
    doubled = number * 2
    print(f'Double element {number} is {doubled}')

# use enumerator if you need the index
for index, number in enumerate(numbers):
    print(f'Index: {index}, Value: {number}')

# Not recommended
length = len(numbers)
for index in range(length):
    print(f'Index: {index}, Value: {numbers[index]}')

# Not recommended
index = 0
while index < len(numbers):
    print(f'Index: {index}, Value: {numbers[index]}')
    index += 1

days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']

# index from 0 to 5, excluding 5
weekday = days[0:5] 
print(f'Weekdays are: {weekday}')

# default start is 0
weekday2 = days[:5] 
print(f'Weekdays version 2 are: {weekday}')

weekends = days[5:7]
print(f'Weekends are {weekends}')

# default end is the length
weekends2 = days[5:] 
print(f'Weekends version 2 are {weekends}')

odd_days = days[::2] 
print(f'Odd days are {odd_days}')

days = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun']
weekday = days[:5] 
today = 'Thu'

is_weekday = today in weekday
print(f'Today is {today}. Is weekday: {is_weekday}')
is_weekend = today not in weekday
print(f'Today is {today}. Is weekend: {is_weekend}')

tens = [10, 20, 30]
hundreds = [500, 600, 700]
all = tens + hundreds
print(all)

repeated_tens = tens * 3
print(repeated_tens)

numbers = [3, 5, 7]
length = len(numbers)
smallest = min(numbers)
biggest = max(numbers)
total = sum(numbers)
print(f'Length: {length}, Min: {smallest}, Max: {biggest}, Sum: {total}')

numbers = [3, 5, 7]
n2 = numbers
n3 = numbers[:2]
numbers.append(42) 
print(numbers) # [3, 5, 7, 42]

if (5 in numbers):
    print(numbers.index(5)) # 1


numbers.insert(1, 50)
print(numbers) # [3, 50, 5, 7, 42]

numbers.sort()
print(numbers) # [3, 5, 7, 42, 50]
print(n2)
print(n3)

numbers = [1, [2, 3], [4, 5, 6]]
numbers[1].append(42)
del numbers[2][2]
print(numbers)

def report_sum(numbers):
    numbers.append(10)
    print(sum(numbers))

scores = [3, 5, 7]
print(f"before call scores are {scores}")

report_sum(scores)
print(f"after call scores are {scores}")

def report_sum2(numbers):
    new_numbers = numbers.copy()
    new_numbers.append(10)
    print(sum(new_numbers))

scores = [3, 5, 7]
print(f"before call scores are {scores}")

report_sum2(scores)
print(f"after call scores are {scores}")

numbers = [1, 2, 3]
numbers.append(37)
numbers.append(42)
top = numbers.pop()
print(top)

# create a tuple 
person1 = "Alice", 19
print(person1[0]) # Alice

# you can create a tuple in parentheses
person2 = ("Bob", 20)

person1 == person2 # False

name, age = person1
print(name, age) # Alice, 19

# an empty tuple
empty = ()

# a tuple with one element
one = 1,

numbers = 1, 2, 3, 4, 5
print(numbers[0]) # 1
print(numbers[::2]) # (1, 3, 5)
print(max(numbers)) # 5

first, second, *rest = numbers
print(first, second, rest)

first, _ = numbers
print(first) # 1

alice = "Alice", [3, 4, 5]
alice[1].append(42)
print(alice) # ('Alice', [3, 4, 5, 42])

# however, you cannot using the assignment to change tuple element
# both give TypeError:  you cannot using the assignment to change tuple element
alice[0] = "Bob"
alice[1] += 42

fruits = {"apple", "orange", "banana"}

numbers = {1, 2, 3, 2, 3, 5}  # set removes duplicated elements
print(numbers) # 1, 2, 3, 5

odds = set(range(1, 6, 2))
print(odds) # 1, 3, 5

odds = [1, 3, 5]
evens = [2, 4]

# TypeError because mutable object
my_set = {odds, evens}

# now it works
odds_2 = (1, 3, 5)
evens_2 = (2, 4)
my_set = {odds_2, evens_2}

fruits = {"apple", "orange", "banana"}
print("apple" in fruits) # True
print("kiwi" in fruits) # False

fruits.add('kiwi') 
fruits.add("apple") # redundant, ignored 
fruits.remove("apple")

more_fruits = {"kiwi", "pear"}

print(fruits) # {'banana', 'kiwi', 'orange'}
print(more_fruits) # {'pear', 'kiwi'}

# union
print(fruits | more_fruits) # {'orange', 'banana', 'pear', 'kiwi'}
# difference
print(fruits - more_fruits) # {'orange', 'banana'}

empty_dict = {}
print(empty_dict)

students = {90: 'Alice', 27: 'Bob', 50: 'Cindy'}
print(students)

more_students = {90: 'Alice', 27: 'Bob', 90: 'Cindy', 200: 'Mike'}
print(more_students)


# use the dict() built-in function
students = dict([(90, 'alice'),  (27,  'bob')])
print(students)

my_dict = dict(A='alice', B='Bob')
print(my_dict)

students = {90: 'Alice', 27: 'Bob', 50: 'Cindy'}

# read a value for a key
name_with_id_90 = students[90]
print(name_with_id_90)

# change a value for a key
students[90] = 'Mike'
print(students[90])

# add a new key-value pair because 97 doesn't exist
students[97] = 'Bill'
print(students)

# reading a value for a non-exist key throws a KeyError exception
name_nobody = students[404]

month_days = {'Jan': 31, 'Apr': 30, 'Jul': 31}

print(f'It has {len(month_days)} elements')

if 'Jan' in month_days:
    print('Jan is in the dictionary')

if 'Feb' not in month_days:
    print('Feb is not in the dictionary')


if 'Jan' in month_days:
    del month_days['Jan']
    print(month_days)

# throw a KeyError exception because the key doesn't exist
del month_days['Jan']
print(month_days)

month_days = {"Jan": 31, "Apr": 30, "Jul": 31}

for month in month_days:
    print(f'{month} has {month_days[month]} days')


for month, days in month_days.items():
    print(f'{month} has {days} days')

days_sequence = month_days.values()
for days in days_sequence:
    print(days, end=' ')
print()

for key in month_days.keys():
    print(f'Month key is {key}', end='; ')
print()

import math 

roots = []
for number in range(5):
    roots.append(math.sqrt(number))

print(roots)

import math

numbers = range(5)

# you need to use list() to get the list result
roots = list(map(math.sqrt, numbers))
print(roots)

import math

roots = [math.sqrt(number) for number in range(5)]

print(roots)

lower_letters = [char for char in "Hello World" if char.islower()]
print(lower_letters) # ['e', 'l', 'l', 'o', 'o', 'r', 'l', 'd']

lower_letters = {char for char in "Hello World" if char.islower()}
print(lower_letters) # {'d', 'e', 'r', 'l', 'o'}


squares = { number: number * number for number in range(5)}
print(squares) # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

def squares(size):
    for number in range(size):
        yield number * number


five_squares = [square for square in squares(5)]
print(five_squares) # [0, 1, 4, 9, 16]

squares = (number * number for number in range(5))
for square in squares:
    print(square, end=", ") 

# output: 0, 1, 4, 9, 16,

Features	List	Tuple	Dictionary	Set
Eample	[1, 2, 3]	('apple', 3)	{'name': 'Alice', 'age': 7}	{2, 4}
Mutable?	Mutable	Immutable	Mutable	Mutable
Mutable element?	Yes	Yes	Key: No, Value: yes	No
Ordered?	Ordered	Ordered	Preserves order since Python 3.7	Unordered
Search time	O(n)	O(n)	O(1)	O(1)

Collection¶

Data Types¶

Comparison¶

When to use which?¶

Creating New Collections From Existing Ones¶

1 String¶

1.1 Built-in String Operations¶

1.2 Slicing¶

1.3 Common String Methods¶

2 List¶

2.1 Creating A List¶

2.2 Basic Operations¶

2.2.1 Index¶

2.2.2 Unpack a List¶

2.2.3 Accessing All Elements¶

2.2.4 Slicing a List¶

2.3 List and Built-in Operations¶

2.4 List Methods¶

Method Examples¶

2.5 Nested List¶

2.6 List as Mutable Argument¶

2.7 A Stack¶

3 Tuple¶

Tuple Operations¶

Tuple Is Immutable, But¶

4 Set¶

4.1 Create a Set¶

4.2 Immutable Elements in Set¶

4.3 Set Operations¶

5 Dictionary¶

5.1 Create a Dictionary¶

5.2 Read or Write a Dictionary Element¶

5.3 Other Operations¶

5.4 Iterate a Dictionary¶

5.5 More Methods¶

6 Creating New Collections From Existing Ones¶

6.1 Motivation¶

6.2 List Comprehension¶

6.3 Filtering Elements¶

6.4 Set and Dictionary Comprehensions¶

7 Generator Object¶

7.1 Why Generator?¶

7.2 Generator Expression¶