[[List]] []
[[Tuple]] ()
[[Set]] {}
[[Dictionary]] {'':}
Dictionary
# Literal syntax for creating a dictionary
scores = {'Luo Hao': 95, 'Bai Yuanfang': 78, 'Di Renjie': 82}
print(scores)
# Constructor syntax for creating a dictionary
items1 = dict(one=1, two=2, three=3, four=4)
# Create a dictionary by zipping two sequences together
items2 = dict(zip(['a', 'b', 'c'], '123'))
# Dictionary comprehension syntax
items3 = {num: num ** 2 for num in range(1, 10)}
print(items1, items2, items3)
# Retrieve values from the dictionary using keys
print(scores['Luo Hao'])
print(scores['Di Renjie'])
# Iterate over all key-value pairs in the dictionary
for key in scores:
print(f'{key}: {scores[key]}')
# Update elements in the dictionary
scores['Bai Yuanfang'] = 65
scores['Zhuge Wanglang'] = 71
scores.update(ColdFace=67, Fang Qihé=85)
print(scores)
if 'Wu Zetian' in scores:
print(scores['Wu Zetian'])
print(scores.get('Wu Zetian'))
# The get method retrieves the corresponding value using a key but allows specifying a default value
print(scores.get('Wu Zetian', 60))
# Remove elements from the dictionary
print(scores.popitem())
print(scores.popitem())
print(scores.pop('Luo Hao', 100))
# Clear the dictionary
scores.clear()
print(scores)
List
Defining lists, iterating through lists, and performing index operations on lists
list1 = [1, 3, 5, 7, 100]
print(list1) # [1, 3, 5, 7, 100]
# The multiplication operator repeats list elements
list2 = ['hello'] * 3
print(list2) # ['hello', 'hello', 'hello']
# Compute the length (number of elements) of the list
print(len(list1)) # 5
# Index (subscript) operations
print(list1[0]) # 1
print(list1[4]) # 100
# print(list1[5]) # IndexError: list index out of range
print(list1[-1]) # 100
print(list1[-3]) # 5
list1[2] = 300
print(list1) # [1, 3, 300, 7, 100]
# Iterate through list elements using indices in a loop
for index in range(len(list1)):
print(list1[index])
# Iterate through list elements using a for loop
for elem in list1:
print(elem)
# Use the enumerate function to iterate through the list and obtain both index and value simultaneously
for index, elem in enumerate(list1):
print(index, elem)
Slicing
fruits = ['grape', 'apple', 'strawberry', 'waxberry']
fruits += ['pitaya', 'pear', 'mango']
# List slicing
fruits2 = fruits[1:4]
print(fruits2) # apple strawberry waxberry
# Perform a full slice to copy the list
fruits3 = fruits[:]
print(fruits3) # ['grape', 'apple', 'strawberry', 'waxberry', 'pitaya', 'pear', 'mango']
fruits4 = fruits[-3:-1]
print(fruits4) # ['pitaya', 'pear']
# Perform reverse slicing to obtain a reversed copy of the list
fruits5 = fruits[::-1]
print(fruits5) # ['mango', 'pear', 'pitaya', 'waxberry', 'strawberry', 'apple', 'grape']
Set
Creating sets
# Literal syntax for creating a set
set1 = {1, 2, 3, 3, 3, 2}
# Constructor syntax for creating a set (explained in detail in the object-oriented section)
set2 = set(range(1, 10))
set3 = set((1, 2, 3, 3, 2, 1))
# Set comprehension syntax (comprehensions can also be used to generate sets)
set4 = {num for num in range(1, 100) if num % 3 == 0 or num % 5 == 0}
Adding and removing elements
set1.add(4)
set1.add(5)
set2.update([11, 12])
set2.discard(5)
if 4 in set2:
set2.remove(4)
print(set1, set2)
print(set3.pop())
print(set3)
Intersection, union, and difference operations
# Intersection, union, difference, and symmetric difference operations on sets
print(set1 & set2)
# print(set1.intersection(set2))
print(set1 | set2)
# print(set1.union(set2))
print(set1 - set2)
# print(set1.difference(set2))
print(set1 ^ set2)
# print(set1.symmetric_difference(set2))
# Check for subsets and supersets
print(set2 <= set1)
# print(set2.issubset(set1))
print(set3 <= set1)
# print(set3.issubset(set1))
print(set1 >= set2)
# print(set1.issuperset(set2))
print(set1 >= set3)
# print(set1.issuperset(set3))
Conversions among Lists, Tuples, Sets, Dictionaries, and Strings
Transcoded by Jianyue SimpRead; original article at zhuanlan.zhihu.com
- Converting between lists and tuples
# Convert a list to a tuple
li = [1, 2, 3]
t = tuple(li)
print(t, type(t))
# Output: (1, 2, 3) <class 'tuple'>
# Convert a tuple to a list
tu = (1, 2, 3)
li = list(tu)
print(li, type(li))
# Output: [1, 2, 3] <class 'list'>
- Converting between lists and strings
# Convert a list to a string
li = ['H', 'e', 'l', 'l', 'o']
str1 = ''.join(li)
print(str1, type(str1))
# Output: Hello <class 'str'>
# Convert a string to a list
str2 = 'hello python'
li1 = str2.split(' ')
print(li1, type(li1))
# Output: ['hello', 'python'] <class 'list'>
- Converting between lists and dictionaries
# Method 1: Convert lists to a dictionary
list1 = ['name', 'age', 'sex']
list2 = ['Zhang San', 18, 'male']
dict = {}
for i in range(len(list1)):
dict[list1[i]] = list2[i]
print(dict, type(dict))
# Output: {'name': 'Zhang San', 'age': 18, 'sex': 'male'} <class 'dict'>
# Method 2: Convert lists to a dictionary using the built-in zip function
list1 = ['name', 'age', 'sex']
list2 = ['Zhang San', 18, 'male']
d = dict(zip(list1, list2))
print(d)
# Convert a dictionary to a list
dict = {'name': 'Zhang San', 'age': 18, 'sex': 'male'}
keys = list(dict.keys())
values = list(dict.values())
print(keys, type(keys))
print(values, type(values))
- Convert a nested list to a dictionary
list3 = [['key1','value1'],['key2','value2'],['key3','value3']]
print(dict(list3))
- Converting between lists and sets
# Convert a list to a set
list1 = [1, 3, 4, 3, 2, 1]
s1 = set(list1)
print(s1, type(s1))
# Output: {1, 2, 3, 4} <class 'set'>
# Convert a set to a list
list2 = list(s1.intersection(s1))
print(list2, type(list2))
# Output: [1, 2, 3, 4] <class 'list'>
- Converting between tuples and strings
# Converting a tuple to a string follows the same method as converting a list to a string
# To convert a string to a tuple, first convert it to a list, then convert that list to a tuple
list = []
a = 'Hello'
list.append(a)
print(list)
b = tuple(list)
print(b, type(b))
# Output: ('Hello',) <class 'tuple'>
- Converting between tuples and dictionaries
# Convert a dictionary to a tuple
dict = {'name': 'Xiao Ming', 'age': 18}
tup = tuple(dict)
print(tup) # Only keys are converted
tup2 = tuple(dict.values())
print(tup2)
# A tuple cannot be directly converted to a dictionary
- Converting between dictionaries and strings
# Convert a dictionary to a string
dic1 = {'a': 1, 'b': 2}
str1 = str(dic1)
# Output: {'a': 1, 'b': 2} <class 'str'>
# Convert a string to a dictionary
dic2 = eval("{'name':'Xiao Ming', 'age':18}")
print(dic2, type(dic2))
- Converting between strings and sets
# Convert a string to a set
str1 = 'hello'
s1 = set(str1)
print(s1, type(s1))
# Output: {'e', 'o', 'h', 'l'} <class 'set'>
- Swapping dictionary keys and values
dic1 = {'a': 1, 'b': 2, 'c': 3}
dic2 = {value: key for key, value in dic1.items()}
print(dic2)