18个Python入门经典必背的程序分享

print("Hello World!") 

def square_sum(numbers): sum = 0 for num in numbers: sum += num ** 2 return sum ​​​​​​​print(square_sum([1, 2, 3, 4])) # 输出 30 

# 计算简单数学表达式 def calculate(expression): return eval(expression) # 用户输入数学表达式 expression = input("请输入一个数学表达式：") # 计算并输出结果 print("结果是：", calculate(expression)) 

# Define a string string = "Hello World!" # Print the original string print("Original string:", string) # Get the length of the string string_length = len(string) print("Length of the string:", string_length) # Concatenate two strings new_string = string + " How are you?" print("Concatenated string:", new_string) # Repeat the string repeated_string = string * 3 print("Repeated string:", repeated_string) # Get a substring substring = string[0:5] print("Substring:", substring) # Replace a substring replaced_string = string.replace("Hello", "Hi") print("Replaced string:", replaced_string) # Check if a string contains a substring is_hello_there = "Hello there!" if "Hello" in is_hello_there: print("'Hello' is in the string.") else: print("'Hello' is not in the string.") 

if condition: # Execute this block if the condition is true else: # Execute this block if the condition is false 

x = int(input("Enter a number: ")) if x > 0: print("Positive number") elif x <0: print("negative number") else: print("zero") < pre>

fruits = ["apple", "banana", "cherry"] for fruit in fruits: print("I like", fruit) 

i = 1 while i <= 10: print(i) i += 1 

def say_hello(name): """ 输出Hello，加上参数 """ print("Hello, " + name)

say_hello("Tom") 

a = [1, 2, 3, 4] 

a = [1, 2, 3, 4] print(a[0]) # 输出 1 

a = [1, 2, 3, 4] a[0] = 5 print(a) # 输出 [5, 2, 3, 4] 

a = [1, 2, 3, 4] del a[0] print(a) # 输出 [2, 3, 4] 

a = [1, 2, 3, 4] print(len(a)) # 输出 4 

a = [1, 2, 3] b = [4, 5, 6] c = a + b print(c) # 输出 [1, 2, 3, 4, 5, 6] d = a * 3 print(d) # 输出 [1, 2, 3, 1, 2, 3, 1, 2, 

d = {key1 : value1, key2 : value2 } 

dict[key] = value 

dict[key] 

dict[key] = value 

del dict[key] 

key in dict 

# 创建字典 dict1 = {'name': 'John', 'age': 30, 'gender': 'male'} # 访问字典中的值 print(dict1['name']) # John # 修改字典中的值 dict1['age'] = 40 print(dict1) # {'name': 'John', 'age': 40, 'gender': 'male'} # 删除字典中的键值对 del dict1['gender'] print(dict1) # {'name': 'John', 'age': 40} # 判断字典中是否包含某个键 print('name' in dict1) # True 

f = open("filename.txt", "r") content = f.read() f.close() 

f = open("filename.txt", "w") f.write("Some text") f.close() 

f = open("filename.txt", "a") f.write("Some more text") f.close() 

with open("filename.txt", "r") as f: content = f.read() 

with open("filename.txt", "r") as f: line = f.readline() 

def bubble_sort(arr): n = len(arr) for i in range(n): for j in range(0, n-i-1): if arr[j] > arr[j+1]: arr[j], arr[j+1] = arr[j+1], arr[j] return arr

def quick_sort(arr, low, high): if low 

def sequential_search(arr, x): for i in range(len(arr)): if arr[i] == x: return i return -1 

def binary_search(arr, x): low = 0 high = len(arr) - 1 while low <= high: mid = (low + high) // 2 if arr[mid] == x: return mid elif arr[mid] 

class Queue: def __init__(self): self.items = [] def is_empty(self): return self.items == [] def enqueue(self, item): self.items.append(item) def dequeue(self): return self.items.pop(0) def size(self): return len(self.items) 

class Stack: def __init__(self): self.items = [] def is_empty(self): return self.items == [] def push(self, item): self.items.append(item) def pop(self): return self.items.pop() def size(self): return len(self.items) 

import requests from bs4 import BeautifulSoup url = 'https://www.example.com/' page = requests.get(url) soup = BeautifulSoup(page.content, 'html.parser') text = soup.get_text() print(text)