python_day1

算术运算

// 只返回整数部分

% 只返回余数

**幂运算

列表方法

In [1]: #向列表添加元素In [2]: member = [1,2,3,]In [3]: member.append(4)In [4]: member
Out[4]: [1, 2, 3, 4]In [5]: #获取列表长度In [6]: len(member)
Out[6]: 4In [7]: member.append?
Signature: member.append(object, /)
Docstring: Append object to the end of the list.
Type:      builtin_function_or_methodIn [8]: append?
Object `append` not found.In [9]: #扩展列表In [10]: member.extend([1,2])In [11]: member
Out[11]: [1, 2, 3, 4, 1, 2]In [12]: #参数必须是列表In [13]: #insert(位置，元素)In [14]: member.insert(1,"牡丹")In [15]: member
Out[15]: [1, '牡丹', 2, 3, 4, 1, 2]In [16]:

匿名函数lambda

**lambda的使用：**关键是给匿名函数赋值
精简代码，调用次数少的函数用lambda就可以了

In [16]: def ds(x):...:     return 2*x+1...:In [17]: ds(5)
Out[17]: 11In [18]: lambda x:2*x+1
Out[18]: <function __main__.<lambda>(x)>In [19]: g=lambda x:2*x+1In [20]: g(5)
Out[20]: 11
In [21]: def add(x,y):...:     return x+y...:In [22]: add_1=lambda x,y:x+yIn [23]: add_1(1,2)
Out[23]: 3

filter/map

filter筛选true/map映射

In [24]: #filter过滤器In [25]: help(filter)
Help on class filter in module builtins:class filter(object)|  filter(function or None, iterable) --> filter object||  Return an iterator yielding those items of iterable for which function(item)|  is true. If function is None, return the items that are true.||  Methods defined here:||  __getattribute__(self, name, /)|      Return getattr(self, name).||  __iter__(self, /)|      Implement iter(self).||  __next__(self, /)|      Implement next(self).||  __reduce__(...)|      Return state information for pickling.||  ----------------------------------------------------------------------|  Static methods defined here:||  __new__(*args, **kwargs) from builtins.type|      Create and return a new object.  See help(type) for accurate signature.In [26]: filter(None,[1,0,True,False])
Out[26]: <filter at 0x4cdb2c8>In [27]: list( filter(None,[1,0,True,False]))
Out[27]: [1, True]In [28]: #筛选奇数的filterIn [29]: def odd(x):...:     return x%2...:In [30]: temp=range(10)In [31]: filter(odd,temp)#只需要传入函数名即可，第二个参数是函数的参数，筛选tru...: e的值
Out[31]: <filter at 0x4d26c08>In [32]: show = filter(odd,temp)In [33]: list(show)
Out[33]: [1, 3, 5, 7, 9]In [34]: #代码精简版In [35]: list(filter(lambda x:x%2,range(10)))
Out[35]: [1, 3, 5, 7, 9]In [36]: #map映射In [37]: list(map(lambda x:x*2,range(10)))
Out[37]: [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

文件

 Character Meaning--------- ---------------------------------------------------------------'r'       open for reading (default)'w'       open for writing, truncating the file first'x'       create a new file and open it for writing'a'       open for writing, appending to the end of the file if it exists'b'       binary mode't'       text mode (default)'+'       open a disk file for updating (reading and writing)'U'       universal newline mode (deprecated)

help(open)

In [2]: f = open("nihao.txt")In [3]: f
Out[3]: <_io.TextIOWrapper name='nihao.txt' mode='r' encoding='cp936'>In [4]: f.read()
Out[4]: '111111111111111\n22222222222222\n3333333333333333\n444444444444444\n555
5555555555555\nxxxxxxxxxxxx\ndddddddddddddddddd\nffffffffffffffffffff\nggggggggg
gggggggggggg\nrrrrrrrrrrrrrrrrrrrrrr\njjjjjjjjjjjjjjjjjj'In [5]: list(f)
Out[5]: []In [6]: list(f)
Out[6]: []In [7]: f.close()In [8]: f = open("nihao.txt")In [9]: f.read(5)
Out[9]: '11111'In [10]: f.tell()
Out[10]: 5In [11]: help(f.seek)
Help on built-in function seek:seek(cookie, whence=0, /) method of _io.TextIOWrapper instanceChange stream position.Change the stream position to the given byte offset. The offset isinterpreted relative to the position indicated by whence.  Valuesfor whence are:* 0 -- start of stream (the default); offset should be zero or positive* 1 -- current stream position; offset may be negative* 2 -- end of stream; offset is usually negativeReturn the new absolute position.In [12]: f,seek(30,0)
---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-12-8c5a4658ebdf> in <module>
----> 1 f,seek(30,0)NameError: name 'seek' is not definedIn [13]: f = open("nihao.txt")In [14]: f.read(5)
Out[14]: '11111'In [15]: f.tell()
Out[15]: 5In [16]: f.seek(30,0)
Out[16]: 30In [17]: f.readline()
Out[17]: '2\n'In [18]: f.write('hello world')
---------------------------------------------------------------------------
UnsupportedOperation                      Traceback (most recent call last)
<ipython-input-18-9347961d9f7c> in <module>
----> 1 f.write('hello world')UnsupportedOperation: not writableIn [19]: f.close()In [20]: f = open("nihao.txt",'w')In [21]: f.write('hello world')
Out[21]: 11In [22]: f.close()

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python_day1

目录

算术运算

列表方法

匿名函数lambda

filter/map

文件

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