python 基础教程之2 字符串操作，变量

0x04 字符串操作

字符串可以直接用+连接
```
>>> 'good'+"good"
'goodgood'
```

数字在加引号以后也是按照字符串来处理

>>> '2'+'2'
'22'

>>> 1+'2'+3+'4'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'

字符串在print 函数里面*就是打印几倍的关系

>>> print('abc\n'*3)
abc
abc
abc

>>> print('abc'*3)
abcabcabc

单个字母不可以*也不可以+

>>> print(a*3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined

在print函数里面数字的*就是*的关系来处理

>>> print(4*3)
12

>>> 4*'222'
'222222222222'

>>> 4*'abc'
'abcabcabcabc'

不可以用浮点型来进行*操作

>>> 4.0*'abc'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't multiply sequence by non-int of type 'float'

字符串与字符串*操作无效

>>> '17'*'21'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: can't multiply sequence by non-int of type 'str'

在print函数里面+操作是无效的，不属于标准输入

>>> print('abc'+3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Can't convert 'int' object to str implicitly

>>> print(a+3)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined

在print函数里面字符串可以相加
```
>>> print('abc'+'3')
abc3
```

0x05 变量

变量可以写在print里面

>>> x=7
>>> print(x)
7
>>> print(x+3)
10
>>> print(x)
7

字符串加双引号赋值变量

>>> x = cde
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'cde' is not defined

>>> x = "cde"
>>> print(x * 3)
cdecdecde
>>>

同名变量被覆盖写入

>>> x = 123
>>> print(x)
123
>>> x = 'abc'
>>> print(x)
abc

变量名称
python中的名字只能以包含字母，数字，下划线，且不能以数字开头

python的变通是通过名称来占位的不用的可以用del删掉

>>> foo = 'avc'
>>> foo
'avc'
>>> del foo
>>> foo
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'foo' is not defined

pyhon支持 in-place操作如下

>>> x = 1
>>> x +=1
>>> x
2

>>> x = 'abc'
>>> x +='fgd'
>>> x
'abcfgd'

linux python基础教程 python 3.5

0x04 字符串操作

0x05 变量

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