python基础-day09

先讲点别的，

问题，自己先思考，百度或者看源码，不行再问，

在公司，新框架，你都问吗？特别是最好别问老板或者高级的人。

def open(file, mode='r', buffering=None, encoding=None, errors=None, newline=None, closefd=True): # known special case of open
    """
    Open file and return a stream.  Raise IOError upon failure.
    
    file is either a text or byte string giving the name (and the path
    if the file isn't in the current working directory) of the file to
    be opened or an integer file descriptor of the file to be
    wrapped. (If a file descriptor is given, it is closed when the
    returned I/O object is closed, unless closefd is set to False.)
    
    mode is an optional string that specifies the mode in which the file
    is opened. It defaults to 'r' which means open for reading in text
    mode.  Other common values are 'w' for writing (truncating the file if
    it already exists), 'x' for creating and writing to a new file, and
    'a' for appending (which on some Unix systems, means that all writes
    append to the end of the file regardless of the current seek position).
    In text mode, if encoding is not specified the encoding used is platform
    dependent: locale.getpreferredencoding(False) is called to get the
    current locale encoding. (For reading and writing raw bytes use binary
    mode and leave encoding unspecified.) The available modes are:
    
    ========= ===============================================================
    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)
    ========= ===============================================================
    
    The default mode is 'rt' (open for reading text). For binary random
    access, the mode 'w+b' opens and truncates the file to 0 bytes, while
    'r+b' opens the file without truncation. The 'x' mode implies 'w' and
    raises an `FileExistsError` if the file already exists.
    
    Python distinguishes between files opened in binary and text modes,
    even when the underlying operating system doesn't. Files opened in
    binary mode (appending 'b' to the mode argument) return contents as
    bytes objects without any decoding. In text mode (the default, or when
    't' is appended to the mode argument), the contents of the file are
    returned as strings, the bytes having been first decoded using a
    platform-dependent encoding or using the specified encoding if given.
    
    'U' mode is deprecated and will raise an exception in future versions
    of Python.  It has no effect in Python 3.  Use newline to control
    universal newlines mode.
    
    buffering is an optional integer used to set the buffering policy.
    Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
    line buffering (only usable in text mode), and an integer > 1 to indicate
    the size of a fixed-size chunk buffer.  When no buffering argument is
    given, the default buffering policy works as follows:
    
    * Binary files are buffered in fixed-size chunks; the size of the buffer
      is chosen using a heuristic trying to determine the underlying device's
      "block size" and falling back on `io.DEFAULT_BUFFER_SIZE`.
      On many systems, the buffer will typically be 4096 or 8192 bytes long.
    
    * "Interactive" text files (files for which isatty() returns True)
      use line buffering.  Other text files use the policy described above
      for binary files.
    
    encoding is the name of the encoding used to decode or encode the
    file. This should only be used in text mode. The default encoding is
    platform dependent, but any encoding supported by Python can be
    passed.  See the codecs module for the list of supported encodings.
    
    errors is an optional string that specifies how encoding errors are to
    be handled---this argument should not be used in binary mode. Pass
    'strict' to raise a ValueError exception if there is an encoding error
    (the default of None has the same effect), or pass 'ignore' to ignore
    errors. (Note that ignoring encoding errors can lead to data loss.)
    See the documentation for codecs.register or run 'help(codecs.Codec)'
    for a list of the permitted encoding error strings.
    
    newline controls how universal newlines works (it only applies to text
    mode). It can be None, '', '\n', '\r', and '\r\n'.  It works as
    follows:
    
    * On input, if newline is None, universal newlines mode is
      enabled. Lines in the input can end in '\n', '\r', or '\r\n', and
      these are translated into '\n' before being returned to the
      caller. If it is '', universal newline mode is enabled, but line
      endings are returned to the caller untranslated. If it has any of
      the other legal values, input lines are only terminated by the given
      string, and the line ending is returned to the caller untranslated.
    
    * On output, if newline is None, any '\n' characters written are
      translated to the system default line separator, os.linesep. If
      newline is '' or '\n', no translation takes place. If newline is any
      of the other legal values, any '\n' characters written are translated
      to the given string.
    
    If closefd is False, the underlying file descriptor will be kept open
    when the file is closed. This does not work when a file name is given
    and must be True in that case.
    
    A custom opener can be used by passing a callable as *opener*. The
    underlying file descriptor for the file object is then obtained by
    calling *opener* with (*file*, *flags*). *opener* must return an open
    file descriptor (passing os.open as *opener* results in functionality
    similar to passing None).
    
    open() returns a file object whose type depends on the mode, and
    through which the standard file operations such as reading and writing
    are performed. When open() is used to open a file in a text mode ('w',
    'r', 'wt', 'rt', etc.), it returns a TextIOWrapper. When used to open
    a file in a binary mode, the returned class varies: in read binary
    mode, it returns a BufferedReader; in write binary and append binary
    modes, it returns a BufferedWriter, and in read/write mode, it returns
    a BufferedRandom.
    
    It is also possible to use a string or bytearray as a file for both
    reading and writing. For strings StringIO can be used like a file
    opened in a text mode, and for bytes a BytesIO can be used like a file
    opened in a binary mode.
    """
    pass

昨天讲了文件五种读的方式，

分别是read(), read(n), readfile(),readfiles(),

其中比较好的是第五种，for x in f:  一次读取一行，而且操作简便，

为什么？前四种，有的一次性读取所有内容，特别吃内存，有些操作又比较麻烦，得一次读一点。

#这个是数据
# name:apple price:10 amount:3 year:2012
# name:tesla price:100000 amount:1 year:2013
#这个是要制作的结果
# [{'name':'apple','price':10,'amount':3},
l = []
li = []
with open('boy',encoding='utf-8',mode= 'r') as f1:
    for x in f1:
        l = x.strip().split()
        li.append({'name':l[0].split(':')[1], 'price':int(l[1].split(':')[1]),'amount':int(l[2].split(':')[1])})
print(li)
sum = 0
for x in li:
    sum += x['price']*x['amount']
print(sum)

#上面我自己写的，下面是老师写的，
#如果增加了条目，下面只需要在name_list中增加条目就可以了。
#给你5颗星！！！！！学习这个通用的写法
l1 = []
name_list = ['name','price','amount','year',]
with open('a.txt',encoding='utf-8') as f1:
    for i in f1:
        l2 = i.strip().split()
        #l2 = [apple,10,3,2004]
        dic = {}
        for j in range(len(l2)):
            dic[name_list[j]] = l2[j] # dic[name] = apple dic[price] = 10
        l1.append(dic)
print(l1)

接下来开始讲函数，

def function(): #首先是函数名，与变量命名一样，
    pass        #函数里面最好不要写print，除非你是测试阶段看过程，
    return 1,2,3,[4,4]
#如果没有return，返回的是None，
#return返回一个值的情况，pass没什么好说的，
#return返回多个值，这些值会以元组的形式返回，比如上面print()打印结果就是(1, 2, 3, [4, 4])
print(function())   #打印结果：(1, 2, 3, [4, 4])

# 接下来将函数的传参
# 参数分两类，
# 形参，存在于函数定义的地方，
# 实参，存在于函数调用时候传入参数的地方，


# 关于传参顺序，
# 位置传参，就是按顺序，怎么定义形参的顺序，实参传入也是这个顺序，
# 关键字传参，用“形参名字=实参值”的方式，明确告诉谁是谁的，因此不需要考虑顺序，
# 混合传参，很好想，就是两者的混合，强调！！！关键字传参只能在最后，即位置传参后面


#形参可以设定默认参数，即没有传入值的情况下，默认值；传入值的话，就覆盖。


#三元运算符
#可以理解为if：else：的简写，仅限这一种形式，if的翻版无法适用，
a = 4
b = 3
z = a if a>b else b
print(z)       #打印结果4
#或者可以省略z，写成print(a if a>b else b)


#最后一点，还是不习惯用format()格式化函数，
#f1.write('{}\t{}\n'.format(username,sex))
#顺便回顾前面的知识，在前面加r，就会忽视特殊符号\n和\t，你看见的是什么就打印什么.

#truncate()这个函数这次终于明白了，
with open('boy',encoding='utf-8',mode = 'r+') as f1:
    f1.seek(1)
    f1.truncate(10)
#文件原本内容是AAAAAAAAAAAAAAAAAAAA，即20个A，
#经过这个操作后，文件内容是AAAAAAAAAA，即10个A，
#首先说下，光标位置在1，
#总结：保留前10个字符，其余的截断，


with open('boy',encoding='utf-8',mode = 'r+') as f1:
    f1.seek(1)
    f1.truncate()
#文件原本内容是AAAAAAAAAAAAAAAAAAAA，即20个A，
#经过这个操作后，文件内容是A，即1个A，
#强调下，光标位置在1，
#总结：从光标位置即1开始往后都截断，即保留光标前的内容！！！删除光标后的内容！！！

>>> t = ([1,2])
>>> type(t)
<class 'list'>
>>> t = ([1,2],)
>>> type(t)
<class 'tuple'>
>>> len(t)
1
>>> #一个，影响着是否是定义元组
>>> t = ([1,2],1)
>>> type(t)
<class 'tuple'>
>>> t[1]=2
Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    t[1]=2
TypeError: 'tuple' object does not support item assignment
>>> #这个错误是说明元组不能更改
>>> t[0][0]='Y'
>>> t
(['Y', 2], 1)
>>> #这个操作，是为了说明，元组内的元素并不受元组不能更改的影响
>>> #即元组的不能更改，是针对第一层来说的。
>>>