每日Python五分钟1：变量和简单数据类型

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1、hello world

print("hello python world！")

输出

hello python world！

2、变量

添加一个msg变量

msg = "hello python world!"
print(msg)

输出

hello python world！

修改msg再打印

msg = "hello python world!"
print(msg)
msg = "hello python crash course world!"
print(msg)

输出

hello python world!
hello python crash course world!

①变量名只能包含字母、数字和下划线。变量名可以是字母或下划线打头，但不能以数字开头。例如：msg_1，但不可以是1_msg。
②变量名不可以包含空格，可以使用下划线分隔单词。
③不要将python关键字和函数名用作变量名，如print。

3、字符串

在Python中，用引号括起来的都是字符串，其中的引号可以是单引号，也可以是双引号。

"This is a string"
'This is also a string'
'I told my friend, "Python is my favorite language!"'
"The language 'Python' is named after Monty Python, not the anake."
"One of Python's strengths is its diverse and supportive community."

修改字符串每个单词首字母的大小写

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

输出

Ada Lovelace

修改字符串每个单词所有字母的大小写

name = "Ada Lovelace"
print(name.upper())
print(name.lower())

输出

ADA LOVELACE
ada lovelace

拼接字符串

first_name = "ada"
last_name = "lovelace"
full_name = first_name + " " + last_name
print(full_name)

输出

ada lovelace

使用制表符/换行符添加空白

print("\tPython")
print("Languages:\nPython\nC\nJavaScript")

输出

        Python
Languages:
Python
C
JavaScript

删除空白

favorite_language = "python "
print(favorite_language+"!")
print(favorite_language.rstrip()+"!")
print(favorite_language+"!")

输出

python  !
python!
python  !

字符串避免语法错误（特别是引号匹配）

msg = "One of Python's strengths is its diverse community."
print(msg)

输出

One of Python's strengths is its diverse community.

换个引号

msg = 'One of Python's strengths is its diverse community.'
print(msg)

输出

File "d:/vscode/hello.py", line 74
    message = 'One of Python's strengths is its diverse community.'
                             ^
SyntaxError: invalid syntax

4、数字

整数

# 加减乘除
print(3+6)
print(3-6)
print(3*6)
print(3/6)

输出

乘方

print(3**2)
print(3**3)
print(10**3)

输出

9
27
1000

混合运算

print(2+3*4)
print((2+3)*4)

输出

14
20

浮点数

print(0.1+0.1)
print(0.2+0.2)
print(2*0.1)
print(2*0.2)

输出

0.2
0.4
0.2
0.4

结果包含的小数位数可能是不确定的

print(0.2+0.1)
print(3*0.1)

输出

0.30000000000000004
0.30000000000000004

使用函数str()避免类型错误

msg = "Happy " + age + "rd Birthday!"
print(msg)

输出

Traceback (most recent call last):
    File "d:/vscode/hello.py", line 126, in <module>
    msg = "Happy " + age + "rd Birthday!"
 TypeError: can only concatenate str (not "int") to str

使用str()后

age = 23
msg = "Happy " + str(age) + "rd Birthday!"
print(msg)

输出

Happy 23rd Birthday!