Python语法入门 - 基础

基础数据类型

 

a = 1
print(type(a))
b = 1.2
print(type(b))
c = True
print(type(c))
a = c
print(type(a))
e = "hello"
print(type(e), id(e))

2进制，8进制，16进制

a=0b101
print(a)
b=0o27
print(b)
c=0x1F
print(c)

字符串

#单引号
str1 = 'abc'
#双引号
str2 = "abc"
#多行字符串(3个单引号包住)
str3 = '''line1
line2'''
print(str3)
#多行字符串(3个双引号包住)
str4 = """line1
line2"""
print(str4)

 

注释

单行注释
# 这里是单行注释

'''
多行注释1
多行注释1
'''

"""
多行注释2
多行注释2
"""

 

逻辑运算

a = 2
b = 2.1
c = 2
print("a>0:", a > 0)
print("a<2:", a < 2)
print("a<=2:", a <= 2)
print("a>b:", a > b)
print("a<b:", a < b)
print("a==b:", a == b)
print("a!=b:", a != b)
print("a==c:", a == c)

bool类型

c = True
d = False
print(c or d)
print(c and d)
print(not c)
print("c==1:", c == 1)
print("d==1:", d == 1)
print("d==0:", d == 0)

 

数值运算

常用的就是：加减乘除，模

a = 3
print("a+2:", a + 2)
print("a-2:", a - 2)
print("a%2:", a % 2)
print("a*2:", a * 2)
print("a/2:", a / 2)
print("a//2:", a // 2) #整除
print(a ** 3) #次方
b = 1.1
c = a + b
print("a+b:", c)

 

条件语句

a = 3
if a > 3:
    print("a>3")
elif 3 == a:
    print("a==3")
else:
    print("a<3")

if嵌套

a = 3
b = 1
if 3 == a:
    if b > 1:
        print("a==3, b>1")
    elif 1==b:
        print("a==3, b==1")
    else:
        print("a==3, b<1")
else:
    print("a!=3")

switch语句

a = 3
match a:
    case 1:
        print("one")
    case 2:
        print("two")
    case _:
        print("default")

字符串的switch

a = "abc"
match a:
    case "abc":
        print("123")
    case "def":
        print("456")
    case _:
        print("default")

 

循环语句

for

#0,1,2
for i in range(3):
    print("i:", i)

print("==========")

# 2,3,4
for i in range(2, 5):
    print("i:", i)

print("==========")

#5,4,3
for i in range(5, 2, -1):
    print("i:", i)

for + continue

for i in range(8):
    if i < 3: continue
    print(i)

for + break

for i in range(8):
    if i >= 5: break
    print(i)

for else

for i in range(3):
    print("i:", i)
else:
    print("for loop not break") #for中途break了就不会被执行

foreach

#逐个字符打印
str = "abc"
for c in str:
    print(c) 

while, python中不支持i--, --i或i++, ++i的语法

i = 3
while i > 0:
    print(i)
    i -= 1
else:
    print("while not break")

没有do while语句

 

模块

对应c#中的命名空间，java中的包

import module # 引用模块
import module as module_aliasName # 模块别名
from module import func # 引用模块的某个函数
from module import func1, func2 # 引用模块的多个函数
from module import * # 导入模块所有函数

 

函数

注意：函数的前后要留2行空行

def test_max(a, b):
    if a > b:
        return a
    return b


a = test_max(2.5, 3.1)
print(a)

貌似参数和返回值上的类型没啥用

def test_min(a: int, b: int) -> int:
    if a < b:
        return a
    return b


b = test_min(2.5, 3.1)
print(b)

不支持函数参数重载，后面的会把前面的覆盖掉。

下面的代码test_sum(1, 2)运行会报错

def test_sum(a, b):
    print("a+b:", a+b)
    

def test_sum(a, b, c):
    print("a+b+c:", a+b+c)


test_sum(1, 2, 3)
test_sum(1, 2)

 

一行结束的分号

# 行尾用不用分号都行
print("有分号");
print("没分号")

# 一行放多个print, 此时必须用分号
print("a"); print("b"); print("c")

 

main函数

def main():
    print("hello world")


if __name__ == '__main__':
    print("文件被直接执行")
    main()
else:
    print("文件被import")