Python常用语句

发表于   |   分类于

简介

常见语句：import，赋值，if，while，for，try，with。

import

1
2
3
4
5
6
7
8
9
10
11
#导入re模块
import re

# 导入pandas模块并赋值为变量pd
import pandas as pd

# 导入user_agents包中的parse模块
from user_agents import parse

# 导入re模块的findall方法
from re import findall

赋值

1
2
3
4
5
6
a = 1
a += 1 # a = a + 1
a *= 2 # a = a * 2
a -= 1 # a = a - 1
a /= 2 # a = a / 2
a %= 2 # a = a & 2

if

1
2
3
4
5
6
7
a = 1
if a <= 1:
    print('a<=1')
elif a <= 2:
    print('1<a<=2')
else:
    print('a>2')

while

1
2
3
4
a = 1
while a < 5:
    print(a)
    a += 1

for

continue：跳出本次循环
break：跳出整个for循环

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
# 列表循环
a = list('hello world')
for i in a:
    print(i)

for i in range(len(a)):
    print(a[i])

# 字典循环
a = {'a': 1, 'b': 2, 'c': 3, 'd': 4}

# 对键进行遍历
for i in a:
    print("键:" + i + ",值:" + str(a[i]))

# 对值进行遍历
for i in a.values():
    print(i)

# 对键值对进行遍历
for key, value in a.items():
    print("键:" + key + ",值:" + str(value))

# 对任何一个迭代器进行循环
import re
for i in re.finditer('.bc','abc bbc cbc eds'):
    print(i)

try

1
2
3
4
5
6
7
# a = 1,不声明a=1,下面就会报错
try:
    print(a == 1)
except:
    print('报错了')
finally:
    print('不管有没有报错,最后都要执行')

with

with 语句适用于对资源进行访问的场合，确保不管使用过程中是否发生异常都会执行必要的“清理”操作，释放资源。
下面以操作文件对象为例,不管程序是否发生异常，with在使用完文件后会都会关闭文件。

1
2
with open('yield.py','r') as f:
    print(f.read())

That’s all.
Happy writing!