python代码实例

当提到 Python 代码实例时，这可以涉及各种不同的应用场景。

Hello World:

python
print("Hello, World!")

变量和运算:

python
# 变量和运算
a = 5
b = 3
result = a + b
print(f"The result is: {result}")

条件语句:

python
# 条件语句
age = 18
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

循环:

python
# 循环
for i in range(5):
    print(f"Count: {i}")

函数:

python
# 函数
def greet(name):
    print(f"Hello, {name}!")

greet("Alice")

列表:

python
# 列表
fruits = ["apple", "banana", "orange"]
print("Fruits:", fruits)

字典:

python
# 字典
person = {"name": "John", "age": 25, "city": "New York"}
print("Person:", person)

文件操作:

python
# 文件操作
with open("example.txt", "w") as file:
    file.write("This is an example.")

异常处理:

python
# 异常处理
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

模块导入:

python
# 模块导入
import math
print("Square root of 16:", math.sqrt(16))

面向对象编程:

python
# 面向对象编程
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):
        print(f"{self.name} says Woof!")

my_dog = Dog("Buddy", 3)
my_dog.bark()

多线程:

python
# 多线程
import threading
import time

def print_numbers():
    for i in range(5):
        time.sleep(1)
        print(i)

def print_letters():
    for letter in "ABCDE":
        time.sleep(1)
        print(letter)

thread1 = threading.Thread(target=print_numbers)
thread2 = threading.Thread(target=print_letters)

thread1.start()
thread2.start()

thread1.join()
thread2.join()

Web 开发:

python
# Web 开发
from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(debug=True)

数据科学示例:

python
# 数据科学示例
import pandas as pd
import matplotlib.pyplot as plt

data = {'Name': ['Alice', 'Bob', 'Charlie', 'David'],
        'Age': [25, 30, 35, 40]}
df = pd.DataFrame(data)

plt.bar(df['Name'], df['Age'])
plt.xlabel('Name')
plt.ylabel('Age')
plt.title('Age distribution')
plt.show()

机器学习示例:

python
# 机器学习示例
from sklearn import datasets
from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier

iris = datasets.load_iris()
X_train, X_test, y_train, y_test = train_test_split(iris.data, iris.target, test_size=0.2)

model = KNeighborsClassifier(n_neighbors=3)
model.fit(X_train, y_train)

accuracy = model.score(X_test, y_test)
print(f"Accuracy: {accuracy}")