6 小时 Python 入门

以下操作均在 Windows 环境下进行操作,先说明一下哈

一、安装 Python

1、官网下载 Python

进入官网(https://www.python.org),点击 Downloads,选择要下载的版本:

image-20200517223148826

2、安装 Python

安装时注意下图勾选部分一定要勾选:

image-20200517223527044

二、安装代码编辑器 PyCharm

1、官网下载 PyCharm

进入官网(https://www.jetbrains.com/pycharm),点击 Downloads,选择要下载的版本:

image-20200517223348661

2、安装 PyCharm

设置安装路径之后,一直点 next 即可。

image-20200517224622654

3、优化 PyCharm 使用

三、HelloWorld

创建第一个项目 HelloWorld —> 创建文件 app.py —> 写入代码:

print("HelloWorld")

效果图:

image-20200517225658342

四、Python 语法

看语法部分之前,推荐直接看下面入门练习题,潜移默化中对 Python 基本语法会有一定了解之后,再回来看这一部分,会更加熟悉 Python 的使用!

五、入门练习题

1.打印 10 个 *

使用到表达式

print('*' * 10)

2.打印价格

使用到变量

price = 10
print(price)

3.描述医院病人的信息

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
 
"""
@Time        : 2020/5/18
@Author      : WuGenQiang
@File        : hospital
@Description : 描述医院病人的信息
"""
full_name = 'John Smith'
age = 20
is_new = True

4.接收用户输入,打印问候信息

使用输入函数 input() 进行输入

name = input('what is your name?')
print('Hi ' + name)

测试:

image-20200518092805760

5.打印年龄

使用到强制类型转换

birth_year = input('Birth year: ')
age = 2019 - int(birth_year)
print(age)

使用 type() 打印数据类型:

print(type(birth_year))

6.字符串打印

三种字符串表达形式

course_1 = 'Python for "Beginners"'
print(course_1)
course_2 = "Python is my 'love'"
print(course_2)
course_3 = '''
Hi John
welcome to python world!
'''
print(course_3)

效果呈现:

image-20200518100439122

获取 course_1 的第一个索引值:

print(course_1[0])

获取 course_1 的最后一个索引值:

print(course_1[-1])

那么获取倒数第二个索引值呢:

print(course_1[-2])

返回索引为 0 - 2 的值:

print(course_1[0:3])

返回索引 0 以及 0 之后的所有字符:

print(course_1[0:])

返回索引小于 5 的所有字符:

print(course_1[:5])

返回所有字符:

print(course_1[:])

返回从第 2 位开始,不包括最后一位字符的字符串:

print(course_1[1:-1])

7.格式化字符串

first = 'WuGenQiang'
last = 'happy'
# 字符串拼接
message = first + ' [' + last + '] is a coder'
# 格式化字符串
msg = f'{first} [{last}] is a coder'
print(message)
print(msg)

8.字符串方法使用

(1)len() 函数:求字符串长度

course = 'Python for Beginners'
# 字符串长度
print(len(course))

(2)upper() 函数:转换成大写字母

# 转换成大写字母
print(course.upper())

(3)lower() 函数:转换成小写字母

# 转换成小写字母
print(course.lower())

(4)find() 函数

# 找字符返回第一个匹配的索引值
print(course.find('n'))

找不到返回 -1,并且区分大小写

(5)replace() 函数

# 替换字符
print(course.replace('Beginners', 'Absolute Beginners'))

(6)in 使用:产生布尔值 False or True

# 判断字符串是否在字符串里
print('Python' in course)

9.算术运算符

举例:

print(10 / 3)
print(10 % 3)
print(10 * 3)
# 10 的 3 次方
print(10 ** 3)
 
x = 10
x = x + 3
x += 3
print(x)

思索下面 x 为多少:

x = 10 + 3 * 2 ** 2

答案是 22,因为取幂运算符是优先的,所以先算 2 的 2 次方

  • 取绝对值
print(abs(-2.9))

10.引入数学模块

import math
print(math.floor(2.9))

11.条件语句的使用

使用 if - elif - else

is_hot = False
is_cold = True
if is_hot:
    print("It's a hot day")
elif is_cold:
    print("It's a cold day")
else:
    print("It's a lovely day")
print("Enjoy your day")

当条件多个并且是 “and” 的关系时,使用:

has_high_income = True
has_good_credit = True
if has_good_credit and has_high_income:
    print("Eligible for loan")

若当条件多个并且是 “or” 的关系时,使用:

has_high_income = False
has_good_credit = True
if has_good_credit or has_high_income:
    print("Eligible for loan")

如何使用 “not”,看下面:(not 相当于取反)

has_good_credit = True
has_criminal_record = False
if has_good_credit and not has_criminal_record:
    print("Eligible for loan")

12.打印天气

使用比较运算符

temperature = 30
if temperature > 30:
    print("It's a hot day")
else:
    print("It's a cold day")

13.打印名字是否符合要求

使用比较运算符

name = "James"
if len(name) < 3:
    print("Name must be at least 3 character")
elif len(name) > 50:
    print("Name must be a maximum of 50 character")
else:
    print("Name looks good")

14.判断体重

weight = int(input('weight: '))
unit = input('(L)bs or (K)g: ')
if unit.upper() == "L":
    converted = weight * 0.45
    print(f"You are {converted} kilos")
else:
    converted = weight / 0.45
    print(f"You are {converted} pounds")

15.打印 1 - 5

使用到 while 循环语句或者 for 循环语句

i = 1
while i <= 5:
    print(i)
    i = i + 1
print("Done")

16.猜数(秘密号码)

secret_number = 9
guess_count = 0
guess_limit = 3
while guess_count < guess_limit:
    guess = int(input('Guess: '))
    guess_count += 1
    if guess == secret_number:
        print('You won!')
        break
else:
    print('Sorry, you failed')

17.Car game

command = ""
started = False
 
while True:
    command = input("> ").lower()
    if command == "start":
        if started:
            print("Car is already started!")
        else:
            started = True
            print("Car started...")
    elif command == "stop":
        if not started:
            print("Car is already stopped!")
        else:
            started = False
            print("Car stopped.")
    elif command == "help":
        print("""
        start - to start the car
        stop - to stop the car
        quit - to quit
        """)
    elif command == "quit":
        break
    else:
        print("Sorry, I don't understand that!")

18.for 循环使用

# 打印 Python
for item in 'Python':
    print(item)
 
for item in ['Mosh', 'John', 'Sarah']:
    print(item)
 
for item in [1, 2, 3, 4]:
    print(item)
 
# 使用范围函数 range, range(10) 表示 0 - 9
for item in range(10):
    print(item)
# range(5, 10) 表示 5 - 9
for item in range(5, 10):
    print(item)
# range(5, 10, 2) 表示 5 - 9, 但是 step = 2
for item in range(5, 10, 2):
    print(item)

19.计算价格总量

使用到 for 循环

prices = [10, 20, 30]
total = 0
for price in prices:
    total += price
print(f"Total: {total}")

20.嵌套循环

for x in range(4):
    for y in range(3):
        print(f'({x}, {y})')

画个大大的 “F”

  • 方式一:
numbers = [5, 2, 5, 2, 2]
for x_count in numbers:
    print('x' * x_count)
  • 方式二:
numbers = [5, 2, 5, 2, 2]
for x_count in numbers:
    output = ''
    for count in range(x_count):
        output += 'x'
    print(output)

21.List

names = ['John', 'Bob', 'Mosh', 'Sarah', 'Mary']
print(names)
print(names[:])
print(names[2:])
# 输出第一个索引值
print(names[0])
# 输出最后一个索引值
print(names[-1])

22.List 中找最大值

numbers = [3, 6, 2, 8, 4, 10]
max = numbers[0]
for number in numbers:
    if number > max:
        max = number
print(max)

23.访问矩阵中的各项

matrix = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9]
]
matrix[0][1] = 20
print(matrix[0][1])
for row in matrix:
    for item in row:
        print(item)

24.数组中常用函数调用

numbers = [5, 2, 1, 7, 4]
# 排序(升序)
numbers.sort()
# 逆序
numbers.reverse()
print(numbers)
# 复制拷贝
numbers2 = numbers.copy()
print(numbers2)
# 移除 1
numbers.remove(1)
# 清空
numbers.clear()
# 末尾加入 20
numbers.append(20)
# 在特定位置插入 12
numbers.insert(0, 12)
# 末尾删除
numbers.pop()
# 返回 5 的索引地址
print(numbers.index(12))
print(numbers)
# 输出 50 是否在 numbers 中
print(50 in numbers)
# 输出数字的数量
print(numbers.count(12))
  • 末尾加入数据
numbers = [2, 2, 4, 6, 3, 4, 6, 1]
uniques = []
for number in numbers:
    if number not in uniques:
        uniques.append(number)
print(uniques)

25.元组

numbers = (1, 2, 3)
print(numbers[0])

注意:

coordinates = (1, 2, 3)
# x = coordinates[0]
# y = coordinates[1]
# z = coordinates[2]
# 与上面相同结果
x, y, z = coordinates
print(x)

26.使用字典

  • 案例
customer = {
    "name": "John Smith",
    "age": 30,
    "is_verified": True
}
customer["name"] = "Jack Smith"
print(customer["name"])
print(customer.get("name"))
print(customer.get("host", "123.12.1.1"))
  • 读号码
phone = input("Phone: ")
digits_mapping = {
    "1": "One",
    "2": "Two",
    "3": "Three",
    "4": "Four",
    "5": "Five"
}
output = ""
for ch in phone:
    output += digits_mapping.get(ch, "!") + " "
print(output)

27.输出表情符号

message = input("> ")
words = message.split(' ')
# 调用表情符号
emojis = {
    ":)": "😄",
    ":(": "😣"
}
output = ""
for word in words:
    output += emojis.get(word, word) + " "
print(output)

使用函数:

# !/usr/bin/env python3
# -*- coding: utf-8 -*-
 
"""
@Time        : 2020/5/20
@Author      : WuGenQiang
@File        : testList
@Description : 
"""
def emoji_converter(message):
    words = message.split(' ')
    # 调用表情符号
    emojis = {
        ":)": "😄",
        ":(": "😣"
    }
    output = ""
    for word in words:
        output += emojis.get(word, word) + " "
    return output
message = input("> ")
result = emoji_converter(message)
print(result)

28.函数

  • 先定义函数,然后才能使用:
def greet_user():
    print('Hi, function!')
 
print("Start")
greet_user()
print("Finished")
  • 传参:
def greet_user(name):
    print(f'Hi, {name}')
 
print("Start")
greet_user("John")
print("Finished")
  • 打印数的平方
def square(number):
    return number * number
 
result = square(3)
print(result)

29.异常处理

  • 出现异常,打印错误信息
try:
    age = int(input('Age: '))
    income = 20000
    risk = income / age
    print(age)
except ZeroDivisionError:
    print('Age cannot be 0.')
except ValueError:
    print('Invalid value')

30.注释

# 这是注释:print Sky is blue
print('Sky is blue')
 
# 计算和返回数的平方
def square(number):
    return number * number

31.类的使用

  • 示例 1:
class Point:
    # 初始化
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def move(self):
        print("move")
    def draw(self):
        print("draw")
# point1 = Point()
# point1.draw()
point2 = Point(10, 20)
# point2.x = 20
print(point2.x)
  • 示例 2:
class Person:
    def __init__(self, name):
        self.name = name
    def talk(self):
        print(f"Hi, I am {self.name}")
 
# john = Person()
# john.talk()
john = Person("John Smith")
john.talk()
 
bob = Person("Bob Smith")
bob.talk()

32.继承的使用

# 继承性讲解
class Mammal:
    # Mammal: 哺乳动物
    def walk(self):
        print("walk")
 
 
class Dog(Mammal):
    def bark(self):
        print("bark")
 
class Cat(Mammal):
    pass
 
dog1 = Dog()
dog1.walk()
dog1.bark()

33.调用模块使用

先创建 converters.py:

def lbs_to_kg(weight):
    return weight * 0.45
def kg_to_lbs(weight):
    return weight / 0.45

然后在需要调用的 py 文件中这样写:

import converters
print(converters.kg_to_lbs(70))

初步实现,然后根据需求完成自己的项目吧!

34.从整个模块中导入特定的函数

不需要模块名作为前缀

# import converters
from converters import kg_to_lbs
print(kg_to_lbs(100))

由此,我们可以为之前写的一些功能实现写一个工具文件,包含着各种要实现的功能函数:

比如这样:

举例:实现求最大数

  • (1)创建 utils.py 工具文件,写入:
def find_max(numbers):
    max = numbers[0]
    for number in numbers:
        if number > max:
            max = number
    return max
  • (2)调用使用:
# import utils
from utils import find_max
numbers = [10, 3, 6, 2]
print(find_max(numbers))

35.从包中导入特定的函数

举例:

创建 Python 包 ecommerce,包中创建文件 shhipping.py,如下:

def calc_shipping():
    print("calc shipping")

调用:

  • 第一种方式:
import ecommerce.shipping
ecommerce.shipping.calc_shipping()
  • 第二种方式:
from ecommerce.shipping import calc_shipping
calc_shipping()
  • 第三种方式:
from ecommerce import shipping
shipping.calc_shipping()

36.生成随机值

  • 举例 1:
import random
for i in range(3):
    #打印随机值
    print(random.random())
    #指定范围的随机数
    print(random.randint(10, 20))
  • 举例 2:
import random
 
members = ['John', 'Mary', 'Mosh']
leader = random.choice(members)
print(leader)
  • 举例 3:1 - 6 间自动生成 2 个随机值
import random
 
class Dice:
    def roll(self):
        first = random.randint(1, 6)
        second = random.randint(1, 6)
        return first, second
 
dice = Dice()
print(dice.roll())

37.寻找目录路径

from pathlib import Path
 
path = Path("ecommerce")
print(path.exists())

如果有会输出 True,没有的话就会输出 False,那就使用下面命令创建一个新的目录

path.mkdir()

删除目录

path.rmdir

搜索文件,打印生成器对象

from pathlib import Path
 
path = Path()
print(path.glob('*.*'))

实例:

from pathlib import Path
 
path = Path()
for file in path.glob('*.py'):
    print(file)

显示目录下所有文件

from pathlib import Path
 
path = Path()
for file in path.glob('*'):
    print(file)

38.表格中读取信息

import openpyxl as xl
wb = xl.load_workbook('transactions.xlsx')
sheet = wb['Sheet1']
cell = sheet['A1']
cell = sheet.cell(1, 1)
print(cell.value)

查看数据有多少行:

print(sheet.max_row)

实现图表显示:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
 
"""
@Time        : 2020/5/18
@Author      : WuGenQiang
@File        : app
@Description : 
"""
import openpyxl as xl
wb = xl.load_workbook('test.xlsx')
sheet = wb['Sheet1']
#cell = sheet['A1']
#cell = sheet.cell(1, 1)
#print(cell.value)
print(sheet.max_row)
from openpyxl.chart import BarChart, Reference
for row in range(1, sheet.max_row + 1):
    cell = sheet.cell(row, 3)
    print(cell.value)
    corrected_price = cell.value * 0.9 + 2
    corrected_price_cell = sheet.cell(row, 4)
    corrected_price_cell.value = corrected_price
values = Reference(sheet,
          min_row=1,
          max_row=sheet.max_row,
          min_col=4,
          max_col=4)
chart = BarChart()
chart.add_data(values)
sheet.add_chart(chart, 'E2')
wb.save('test2.xlsx')

效果图:

image-20200526165657549

优化:子函数调用版

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
 
"""
@Time        : 2020/5/18
@Author      : WuGenQiang
@File        : app
@Description : 
"""
import openpyxl as xl
from openpyxl.chart import BarChart, Reference
 
def process_workbook(filename):
    wb = xl.load_workbook(filename)
    sheet = wb['Sheet1']
    # cell = sheet['A1']
    # cell = sheet.cell(1, 1)
    # print(cell.value)
    print(sheet.max_row)
 
    for row in range(1, sheet.max_row + 1):
        cell = sheet.cell(row, 3)
        print(cell.value)
        corrected_price = cell.value * 0.9 + 2
        corrected_price_cell = sheet.cell(row, 4)
        corrected_price_cell.value = corrected_price
    values = Reference(sheet,
                       min_row=1,
                       max_row=sheet.max_row,
                       min_col=4,
                       max_col=4)
    chart = BarChart()
    chart.add_data(values)
    sheet.add_chart(chart, 'E2')
    wb.save(filename)
 
process_workbook('test.xlsx')

39.CSV 文件导入数据

数据集下载:vgsales.csv

整体输出数据

import pandas as pd
#从CSV文件导入数据,存储在df中
df = pd.read_csv('vgsales.csv')
df

效果:

image-20200531195556447

获取数据集的形状

#获取数据集的形状
df.shape

效果:

image-20200531200756673

分段输出数据

#描述方法
df.describe()

效果:

image-20200531201607125

获取值

df.values

效果:

image-20200531202108365

image-20200531204830570

清洁数据

删除数据举例:

import pandas as pd
#从CSV文件导入数据,存储在df中
df = pd.read_csv('vgsales.csv')
x = df.drop(columns=['JP_Sales'])
x

获取某一列数据:

import pandas as pd
#从CSV文件导入数据,存储在df中
df = pd.read_csv('vgsales.csv')
y = df['JP_Sales']
y

40.决策树

import pandas as pd
from sklearn.tree import DecisionTreeClassifier
#从CSV文件导入数据,存储在df中
df = pd.read_csv('vgsales.csv')
x = df.drop(columns=['JP_Sales'])
y = df['JP_Sales']
#树分类器
model = DecisionTreeClassifier()
model.fit(x, y)
#调用模型预测
predictions = model.predict([[41.49, 29.02], [29.08, 3.58]])
predictions

可能数据不对,可以使用其他测试数据

测量数据精确度

数据被分为两组:训练和测试

import pandas as pd
from sklearn.tree import DecisionTreeClassifier
from sklearn.model_selection import train_test_split
from sklearn.metrics import accuracy_score
#从CSV文件导入数据,存储在df中
df = pd.read_csv('vgsales.csv')
x = df.drop(columns=['JP_Sales'])
y = df['JP_Sales']
#培训和测试数据输入输出集
x_train, x_test, y_train, y_test = train_test_split(x, y, test_size=0.2)
#树分类器
model = DecisionTreeClassifier()
model.fit(x_train, y_train)
#调用模型预测
predictions = model.predict(x_test)
score = accuracy_score(y_test, predictions)
score

六、参考资料

[1] 2020 最新 Python 教程 6 小时入门