2 基本数据类型

2.1 变量variable

规则：

变量名只能包含字母、数字、下划线、中文字符等，不能包含空格，且只能以字母或下划线开头，不能以数字开头。
不要用Python关键字和函数名作为变量名。
变量名具有描述性。

创建一个名为message的变量（variable），"Hello python world!"是变量指向的值（value）。

Code

message = "Hello , world!" 

# 直接打印 或 print()
message
print(message)

Hello , world!

2.2 字符串string

用引号引起的是字符串，其中引号既可以是双引号，也可以是单引号。

Code

"This is a string"
'This is also a string'
"他说'世界是你们的，也是我们的，但终究是你们的'。流泪\u1000"

"他说'世界是你们的，也是我们的，但终究是你们的'。流泪က"

2.2.1 使用方法method修改字符串

例如，在函数调用print()中，方法 title() 出现在变量名后面。

method是Python对数据执行的操作，在name.title()中，name是变量名，句点.让Python对name变量执行方法title()指定的操作。

Code

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

ada lovelace
Ada Lovelace
ADA LOVELACE
ada lovelace

'ada lovelace'

method
method	作用
`title()`	以首字母大写的方式显示每个单词
`upper()`	使字母全大写
`lower()`	使字母全小写
`strip()`	删除左右空白
`rstrip()`	删除右空白
`lstrip()`	删除左空白
`removeprefix(x)`	删除前缀x

2.2.2 在字符串中使用变量

f字符串，在左"之前添加字母f （format设置格式），再将变量名放入{}内。

Code

first_name = "ada"
last_name = "lovelace"
full_name = f"{first_name} {last_name}"
print(full_name)
print(f"Hello,{full_name.title()}!")
greet = f"Hello,{full_name.title()}!"
print(greet)

name = "Eric"
message = f"Hello {name},would you like to learn some Python today?"
message

ada lovelace
Hello,Ada Lovelace!
Hello,Ada Lovelace!

'Hello Eric,would you like to learn some Python today?'

2.2.3 使用制表符或换行符添加空白

空白泛指任何非打印字符，如空格、制表符、换行符。

Code

print("Python")
print("\tPython")
print("Languages:\n\t1.Python\n\t2.R\n\t3.C")

Python
    Python
Languages:
    1.Python
    2.R
    3.C

2.2.4 删除空白

Code

language = " python "
language
#删除右空白
language.rstrip()

#删除左空白
language.lstrip()

#删除左右空白
language.strip()

'python'

但这种删除是暂时的

Code

language

' python '

2.2.5 删除前后缀

Code

github_url = "https://github.com"
github_url.removeprefix("https://")

file = "basics.txt"
file.removesuffix(".txt")

'basics'

2.3 数number

2.3.1 整数integer

可执行加+、减-、乘*、除/、整除//、乘方**、求模（取余数） % 运算。

Code

2+3
5-2
2*3
8/2
8//2
9//2
5**2
10%3
print(5+3)
print(9-1)
print(4*2)
print(16//2)
print(2**3)

2.3.2 浮点数float

Code

0.2+0.5
2*0.4
0.2+0.1
3*0.1

4/2
1+2.0
3.0**2

9.0

2.3.3 数中的下划线

位数分组

Code

x = 14_000_000_000
x

14000000000

2.3.4 同时给多个变量赋值

用逗号分隔

Code

x,y,z = 1,2.0,4**2
x
y
z

常量constant

变量名全大写字母表示常量。

Code

FAVORITE_NUMBER = 9
message = f"My favorite number is {FAVORITE_NUMBER}"
print(message)

My favorite number is 9

2.4 Python原则

Code

import this

The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!