python 3.6学习--基础1：数字，字符串，数组，列表的基本使用

来源：官方文档：https://docs.python.org/3.6/tutorial/index.html

都是拷下来自己看的（小白上路的笔记），官方文档更详细...

1，数字：解释器充当一个简单的计算器，您可以在其上键入表达式，它将写入值。

1.1 加减乘除没什么好讲的，贴点示例看看就行

[code]>>> 2 + 2
4
>>> 50 - 5*6
20
>>> (50 - 5*6) / 4
5.0
>>> 8 / 5  # division always returns a floating point number
1.6

有一个不一样的：// 双斜杠可以去掉余数

（

/

）总是返回一个浮点数。要进行分区并获得整数结果（丢弃任何小数结果），您可以使用

//

 运算符; 计算你可以使用的余数

%

：

[code]>>> 17 / 3  # classic division returns a float
5.666666666666667
>>>
>>> 17 // 3  # floor division discards the fractional part
5
>>> 17 % 3  # the % operator returns the remainder of the division
2
>>> 5 * 3 + 2  # result * divisor + remainder
17

还有这个：** 两个星号表示求几次方

[code]>>> 5 ** 2  # 5 squared
25
>>> 2 ** 7  # 2 to the power of 7
128

2.字符串

2.1 Python还可以操作字符串，这可以通过多种方式表达。它们可以用单引号（

'...'

）或双引号（

"..."

）括起来，结果相同， 

\

可用于转义引号

[code]>>> 'spam eggs'  # single quotes
'spam eggs'
>>> 'doesn\'t'  # use \' to escape the single quote...
"doesn't"
>>> "doesn't"  # ...or use double quotes instead
"doesn't"
>>> '"Yes," they said.'
'"Yes," they said.'
>>> "\"Yes,\" they said."
'"Yes," they said.'
>>> '"Isn\'t," they said.'
'"Isn\'t," they said.'

2.2 print()打印没什么讲的，如果让反斜杠正常打印，可以通过在第一个引号之前添加原始字符串来使用原始字符串 

r

[code]>>> print('C:\some\name')  # here \n means newline!
C:\some
ame
>>> print(r'C:\some\name')  # note the r before the quote
C:\some\name

2.3字符串文字可以跨越多行。一种方法是使用三引号： 

"""..."""

或

'''...'''

。行尾自动包含在字符串中，但可以通过

\

在行尾添加a来防止这种情况（差不多就是解决回车就换行提交的尴尬）

[code]print("""\
Usage: thingy [OPTIONS]
-h                        Display this usage message
-H hostname               Hostname to connect to
""")

以上有这样的输出

[code]Usage: thingy [OPTIONS]
-h                        Display this usage message
-H hostname               Hostname to connect to

 2.4 字符串可以做乘法，差不多就是这个意思

[code]>>> # 3 times 'un', followed by 'ium'
>>> 3 * 'un' + 'ium'
'unununium'

 2.5 两个或多个彼此相邻的字符串文字（即引号之间的字符串）会自动连接（神奇）。用 + 也可以连接，后面就不讲了。

[code]>>> 'Py' 'thon'
'Python'

 2.6 想要断开长字符串时，此功能特别有用：（他说很有用）

[code]>>> text = ('Put several strings within parentheses '
...         'to have them joined together.')
>>> text
'Put several strings within parentheses to have them joined together.'

 2.7 字符串可以被索引（下标） ，从0开始。

[code]>>> word = 'Python'
>>> word[0]  # character in position 0
'P'
>>> word[5]  # character in position 5
'n'

 指数也可能是负数，从右边开始计算：

[code]>>> word[-1]  # last character
'n'
>>> word[-2]  # second-last character
'o'
>>> word[-6]
'P'

 还可以截取子串：

[code]>>> word[0:2]  # characters from position 0 (included) to 2 (excluded)
'Py'
>>> word[2:5]  # characters from position 2 (included) to 5 (excluded)
'tho'

 截取时可以省略下标; 省略的第一个索引默认为零，省略的第二个索引默认为要切片的字符串的大小

[code]>>> word[:2]   # character from the beginning to position 2 (excluded)
'Py'
>>> word[4:]   # characters from position 4 (included) to the end
'on'
>>> word[-2:]  # characters from the second-last (included) to the end
'on'

下标超过字符串长度也会报错

[code]>>> word[42]  # the word only has 6 characters
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: string index out of range

 Python字符串无法更改 - 它们是不可变的。因此，分配给字符串中的索引位置会导致错误：

[code]>>> word[0] = 'J'
...
TypeError: 'str' object does not support item assignment
>>> word[2:] = 'py'
...
TypeError: 'str' object does not support item assignment

 内置函数

len()

返回字符串的长度：

[code]>>> s = 'supercalifragilisticexpialidocious'
>>> len(s)
34

 3.列表，数组（好像没区分开）

[code]>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]

 像字符串（以及所有其他内置序列类型）一样，列表可以被索引和切片：

[code]>>> squares[0]  # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:]  # slicing returns a new list
[9, 16, 25]

 列表还支持串联等操作：

[code]>>> squares + [36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

 与不可变的字符串不同，列表是可变 类型，即可以更改其内容：

[code]>>> cubes = [1, 8, 27, 65, 125]  # something's wrong here
>>> 4 ** 3  # the cube of 4 is 64, not 65!
64
>>> cubes[3] = 64  # replace the wrong value
>>> cubes
[1, 8, 27, 64, 125]

 

append()

 方法在列表末尾添加新项目

[code]>>> cubes.append(216)  # add the cube of 6
>>> cubes.append(7 ** 3)  # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]

 也可以分配给切片，这甚至可以改变列表的大小或完全清除它：

[code]>>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> letters
['a', 'b', 'c', 'd', 'e', 'f', 'g']
>>> # replace some values
>>> letters[2:5] = ['C', 'D', 'E']
>>> letters
['a', 'b', 'C', 'D', 'E', 'f', 'g']
>>> # now remove them
>>> letters[2:5] = []
>>> letters
['a', 'b', 'f', 'g']
>>> # clear the list by replacing all the elements with an empty list
>>> letters[:] = []
>>> letters
[]

 内置函数

len()

也适用于列表：

[code]>>> letters = ['a', 'b', 'c', 'd']
>>> len(letters)
4

 可以嵌套列表（创建包含其他列表的列表），例如：

[code]>>> a = ['a', 'b', 'c']
>>> n = [1, 2, 3]
>>> x = [a, n]
>>> x
[['a', 'b', 'c'], [1, 2, 3]]
>>> x[0]
['a', 'b', 'c']
>>> x[0][1]
'b'

 如果你看到这里，我会告诉你原来复制粘贴原来还挺累人的....

 

 

 

阅读更多