Python编程：从入门到实践

一、Python简介

Python是一种面向对象、解释型的高级程序设计语言。Python语言简洁、易读、易学，适用范围广泛，在数据科学、web开发、自动化、机器学习、人工智能等方面都有广泛的应用。Python首次发布于1991年，由Guido van Rossum创建，目前Python的最新版本是3.8.5。

二、Python基础知识

1、Hello World

print("Hello World!")

2、变量和数据类型

message = "Hello Python World!"
print(message)

name = "ada lovelace"
print(name.title())
print(name.upper())
print(name.lower())

3、列表和元组

fruits = ['apple', 'banana', 'orange']
print(fruits)
print(fruits[0])
print(fruits[-1])

dimensions = (200, 50)
print(dimensions[0])
print(dimensions[1])

三、Python进阶

1、函数

def greet_user(username):
    print("Hello, " + username.title() + "!")

greet_user('jesse')

2、类和对象

class Dog():
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def sit(self):
        print(self.name.title() + " is now sitting.")
        
my_dog = Dog('willie', 6)
print(my_dog.name)
print(my_dog.age)
my_dog.sit()

3、文件读写

filename = 'pi_digits.txt'
with open(filename) as file_object:
    contents = file_object.read()
    print(contents.rstrip())

四、Python实战

1、数据可视化

import matplotlib.pyplot as plt

x_values = [1, 2, 3, 4, 5]
y_values = [1, 4, 9, 16, 25]
plt.plot(x_values, y_values)
plt.show()

2、web应用开发

from flask import Flask

app = Flask(__name__)

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

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

3、机器学习

from sklearn import datasets
from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier

iris = datasets.load_iris()
X = iris.data
y = iris.target
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.3)
clf = KNeighborsClassifier()
clf.fit(X_train, y_train)
print(clf.score(X_test, y_test))