Python 基礎部分-4

時間 2020-12-01

標籤 python 程序員 app less ide 函數 this 編碼 spa 欄目 Python 简体版

原文原文鏈接

文件的基本操做python

open()程序員

用於文件處理app

操做文件時，通常須要經歷以下步驟：less

打開文件
操做文件
關閉文件

基本操做文件方式ide

open(文件名/路徑，模式，編碼)，默認模式爲「只讀」函數

f = open('test.log', "r")
data = f.read()
f.close()
print(data)

>>>
testlog

打開文件時，須要指定文件路徑和以何等方式打開文件，打開後，便可獲取該文件句柄，往後經過此文件句柄對該文件操做。ui

打開文件的模式：　this

r ，只讀模式【默認】

f = open('test.log')
data = f.read()
f.close()
 print(data)

>>>
abc123

w，只寫模式【不可讀；文件不存在則建立；文件存在則清空內容；】

f = open('test.log', 'w')
data = f.write('defg123456') #以寫方式覆蓋文件
f.close()
print(data)

>>>
10  #寫入10個字符

f = open('test.log', 'w')
data = f.read()
f.close()
print(data)

>>>
data = f.read()
io.UnsupportedOperation: not readable#只寫方式不能讀取文件內同

x，只寫模式【不可讀；文件不存在則建立；文件存在則報錯】

f = open('test2.log', 'x')#文件不存在，建立一個新的文件
f.write("qwe456") 
f.close()

f = open('test2.log', 'x')
f.write("zxcv123456") 
f.close()

>>>
    f = open('test2.log', 'x')
FileExistsError: [Errno 17] File exists: 'test2.log'#文件已經存在，不能建立同名文件

a，追加模式【不可讀；文件不存在則建立；文件存在則只追加內容；】

f = open('test2.log', 'a')
data = f.write("9876543210")
f.close()
print(data)

>>>
10 #寫入10個字符

"+" 表示能夠同時讀寫某個文件編碼

r+，讀寫【可讀，可寫】

　　　　先讀取文檔，在文檔末尾追加寫入，指針移到最後spa

f = open("test.log", 'r+', encoding = "utf-8")
print(f.tell()) #顯示指針位置，指針從開始向後讀取
f.write("123456")

data = f.read()

print(data)
print(f.tell()) #讀取文件後指針位置

f.close()

>>>
0
123456
6

w+，寫讀【可讀，可寫】

　　　　先把文件內容清空，從開始向後讀取文件；從新寫入內容後，指針移到最後，讀取文件。

f = open("test.log", 'w+', encoding = "utf-8")
f.write("123456")#寫入完成後，文檔指針位置在文件末尾
f.seek(0)#設定指針在文檔開始
data = f.read()
print(data)

x+ ，寫讀【可讀，可寫】

　　　　若文件存在，系統報錯，建新文件，再寫入內容後，指針移到最後，讀取文件。

a+，寫讀【可讀，可寫】

　　　　文件打開同時，文檔指針已經設定在最後，寫入文件後，指針留在文件的最後。

f = open("test.log", 'a+', encodig"utf-8")
f.write("987654")
print(f.tell()) #顯示指針位置
f.seek(0)　　　　#設定指針爲文檔最開始
data = f.read()
print(data) 

>>>
6 
987654

r+ w+ x+ a+都以指針位置讀取或寫入數據。

"b"表示以字節（bytes）的方式操做

rb 或 r+b

f = open('test2.log', 'wb')
f.write(bytes("中國", encoding='utf-8'))
f.close()


f = open('test2.log', "rb")
data = f.read()
f.close()
print(data)
str_data = str(data, encoding='utf - 8')
print(str_data)

>>>
b'\xe4\xb8\xad\xe5\x9b\xbd'
中國

wb 或 w+b

f = open('test2.log', 'wb')
str_data = "中國"
bytes_data = bytes(str_data, encoding = 'utf-8')#指定寫如的編碼
f.write(bytes_data)
f.close()

f = open('test2.log', 'wb')
f.write("中國")
f.close()

>>>
    f.write("中國")
TypeError: a bytes-like object is required, not 'str'

xb 或 x+b
ab 或 a+b

注：以b方式打開時，讀取到的內容是字節類型，寫入時也須要提供字節類型

普通打開方式

python內部將底層010101010的字節轉換成字符串

二進制打開方式

python將讀取將底層010101010的字節再按照程序員設定的編碼，轉換成字符串。

f = open('test2.log', 'wb')
f.write(bytes("中國", encoding='utf-8'))
f.close()

f = open('test2.log', "rb")
data = f.read()
f.close()
print(data)
str_data = str(data, encoding='utf - 8')
print(str_data)

>>>
b'\xe4\xb8\xad\xe5\x9b\xbd'
中國

文件操做內部函數

f.flush()

主動把內容刷新到硬盤內

f = open("test.log", "r+", encoding="utf-8")
f.write("123456789")#內容寫入到內存中
f.flush()#把內容刷新到硬盤內
i = input(">>>")

f.readline()

僅讀取一行內容

f1 = open("test.log", 'r+', encoding = 'utf-8')
d = f1.realline()
f.close()
print(d)

f.tell()

顯示指針位置

f.seek()

設定指針位置

f.trucate()

截取數據，僅保留指針前的數據

f = open("test.log", "r+", encoding = "utf-8")
print(f.tell())
print(f.seek(6))

f.truncate()
f1.close()

f.close()

關閉文件，把文件保存在硬盤中

使用for循環讀取文件

f = open("xxx", "r")
for line in f:
    print(line)

with 循環打開文件

with open("xxx", 'r') as f:
    f.read()

f = open("xxx", 'r') 
f.read()
#不須要f.close()關閉文件

with支持同時打開兩個文件,從源文件中逐行拷貝到目標文件中

with open("test.log", 'r') as obj1, open ("test2.log", 'w') as obj2:
    for line in obj1:
        obj2.write(line)

class file(object)
    def close(self): # real signature unknown; restored from __doc__
        關閉文件
        """
        close() -> None or (perhaps) an integer.  Close the file.
         
        Sets data attribute .closed to True.  A closed file cannot be used for
        further I/O operations.  close() may be called more than once without
        error.  Some kinds of file objects (for example, opened by popen())
        may return an exit status upon closing.
        """
 
    def fileno(self): # real signature unknown; restored from __doc__
        文件描述符  
         """
        fileno() -> integer "file descriptor".
         
        This is needed for lower-level file interfaces, such os.read().
        """
        return 0    
 
    def flush(self): # real signature unknown; restored from __doc__
        刷新文件內部緩衝區
        """ flush() -> None.  Flush the internal I/O buffer. """
        pass
 
 
    def isatty(self): # real signature unknown; restored from __doc__
        判斷文件是不是贊成tty設備
        """ isatty() -> true or false.  True if the file is connected to a tty device. """
        return False
 
 
    def next(self): # real signature unknown; restored from __doc__
        獲取下一行數據，不存在，則報錯
        """ x.next() -> the next value, or raise StopIteration """
        pass
 
    def read(self, size=None): # real signature unknown; restored from __doc__
        讀取指定字節數據
        """
        read([size]) -> read at most size bytes, returned as a string.
         
        If the size argument is negative or omitted, read until EOF is reached.
        Notice that when in non-blocking mode, less data than what was requested
        may be returned, even if no size parameter was given.
        """
        pass
 
    def readinto(self): # real signature unknown; restored from __doc__
        讀取到緩衝區，不要用，將被遺棄
        """ readinto() -> Undocumented.  Don't use this; it may go away. """
        pass
 
    def readline(self, size=None): # real signature unknown; restored from __doc__
        僅讀取一行數據
        """
        readline([size]) -> next line from the file, as a string.
         
        Retain newline.  A non-negative size argument limits the maximum
        number of bytes to return (an incomplete line may be returned then).
        Return an empty string at EOF.
        """
        pass
 
    def readlines(self, size=None): # real signature unknown; restored from __doc__
        讀取全部數據，並根據換行保存值列表
        """
        readlines([size]) -> list of strings, each a line from the file.
         
        Call readline() repeatedly and return a list of the lines so read.
        The optional size argument, if given, is an approximate bound on the
        total number of bytes in the lines returned.
        """
        return []
 
    def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
        指定文件中指針位置
        """
        seek(offset[, whence]) -> None.  Move to new file position.
         
        Argument offset is a byte count.  Optional argument whence defaults to
(offset from start of file, offset should be >= 0); other values are 1
        (move relative to current position, positive or negative), and 2 (move
        relative to end of file, usually negative, although many platforms allow
        seeking beyond the end of a file).  If the file is opened in text mode,
        only offsets returned by tell() are legal.  Use of other offsets causes
        undefined behavior.
        Note that not all file objects are seekable.
        """
        pass
 
    def tell(self): # real signature unknown; restored from __doc__
        獲取當前指針位置
        """ tell() -> current file position, an integer (may be a long integer). """
        pass
 
    def truncate(self, size=None): # real signature unknown; restored from __doc__
        截斷數據，僅保留指定以前數據
        """
        truncate([size]) -> None.  Truncate the file to at most size bytes.
         
        Size defaults to the current file position, as returned by tell().
        """
        pass
 
    def write(self, p_str): # real signature unknown; restored from __doc__
        寫內容
        """
        write(str) -> None.  Write string str to file.
         
        Note that due to buffering, flush() or close() may be needed before
        the file on disk reflects the data written.
        """
        pass
 
    def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
        將一個字符串列表寫入文件
        """
        writelines(sequence_of_strings) -> None.  Write the strings to the file.
         
        Note that newlines are not added.  The sequence can be any iterable object
        producing strings. This is equivalent to calling write() for each string.
        """
        pass
 
    def xreadlines(self): # real signature unknown; restored from __doc__
        可用於逐行讀取文件，非所有
        """
        xreadlines() -> returns self.
         
        For backward compatibility. File objects now include the performance
        optimizations previously implemented in the xreadlines module.
        """
        pass

2.x

Python 2.x

class TextIOWrapper(_TextIOBase):
    """
    Character and line based layer over a BufferedIOBase object, buffer.
    
    encoding gives the name of the encoding that the stream will be
    decoded or encoded with. It defaults to locale.getpreferredencoding(False).
    
    errors determines the strictness of encoding and decoding (see
    help(codecs.Codec) or the documentation for codecs.register) and
    defaults to "strict".
    
    newline controls how line endings are handled. 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 line_buffering is True, a call to flush is implied when a call to
    write contains a newline character.
    """
    def close(self, *args, **kwargs): # real signature unknown
        關閉文件
        pass

    def fileno(self, *args, **kwargs): # real signature unknown
        文件描述符  
        pass

    def flush(self, *args, **kwargs): # real signature unknown
        刷新文件內部緩衝區
        pass

    def isatty(self, *args, **kwargs): # real signature unknown
        判斷文件是不是贊成tty設備
        pass

    def read(self, *args, **kwargs): # real signature unknown
        讀取指定字節數據
        pass

    def readable(self, *args, **kwargs): # real signature unknown
        是否可讀
        pass

    def readline(self, *args, **kwargs): # real signature unknown
        僅讀取一行數據
        pass

    def seek(self, *args, **kwargs): # real signature unknown
        指定文件中指針位置
        pass

    def seekable(self, *args, **kwargs): # real signature unknown
        指針是否可操做
        pass

    def tell(self, *args, **kwargs): # real signature unknown
        獲取指針位置
        pass

    def truncate(self, *args, **kwargs): # real signature unknown
        截斷數據，僅保留指定以前數據
        pass

    def writable(self, *args, **kwargs): # real signature unknown
        是否可寫
        pass

    def write(self, *args, **kwargs): # real signature unknown
        寫內容
        pass

    def __getstate__(self, *args, **kwargs): # real signature unknown
        pass

    def __init__(self, *args, **kwargs): # real signature unknown
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __next__(self, *args, **kwargs): # real signature unknown
        """ Implement next(self). """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    buffer = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    closed = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    encoding = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    errors = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    name = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    newlines = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    _CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    _finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

3.x

Python 3.x

冒泡排序

#利用新變量互換值
a1 = 123
a2 = 456

temp = a1
a1 = a2
a2 = temp

a1 = 456
a2 = 123

#實現列表元組互換
li = [11,33,22,44,55]

temp = li[1]
li[1] = li[2]
li[2]=temp

print(li)

>>>
[11,22,33,44,55]

#把列表裏面的全部值進行比較
li = [33,22,10,1]

for i in range(len(li)-1): #循環列表次數
    # i = 0              1   2   3
    #current:      li[0] 1   2   3
    #next_value:   li[1] 2   3   4 #列表li裏面沒有li[4]，所以須要減小一次循環次數
    current = li[i]
    next_value = li[i+1]
    print(i, current, next_value)

>>>
0 33 2 #第一次循環
1 2 10 #第二次循環
2 10 1 #第三次循環

#循環一次列表，僅把一個最大的元素排在最右方
li = [33,2,10,1]

for i in range(len(li)-1): #循環列表元素
    if li[i] > li[i+1]: #元素互換的條件
        temp = li[i]
        li[i] = li[i+1]
        li[i + 1] = temp
print(li)

>>>
[2, 10, 1, 33]

li = [33,2,10,1]

for i in range(len(li)-1): #元素內部從左往右循環比較三次，等於列表長度減1那麼屢次，如列表4個元素，兩兩比較，須要比較三次1-(33, 2), 2-(2,10), 3-(10, 1)

    if li[i] > li[i+1]:
        temp = li[i]
        li[i] = li[i+1]
        li[i + 1] = temp

print(li)

>>>
[2,10,1,33]

li = [33,2,10,1]
for j in range(1, len(li)): #因爲i循環每完成一次，下一次i循環排序的元素就減小一次， j的數值應爲1,2,3 到數列的長度爲止。
    #j: 1 ,2 ,3, i循環中兩兩比較的次數
    for i in range(len(li)-j): #元素內部循環比較完成一次，獲得最右邊的一個最大元素，下一次循環比較的元素就減小一個，j表明每次完成循環減小的排序的元素。
        if li[i] > li[i+1]:
            temp = li[i]
            li[i] = li[i+1]
            li[i + 1] = temp

print(li)

>>>
[1, 2, 10, 33]

遞歸

遞歸指的是這樣一個數列：一、一、二、三、五、八、1三、2一、……

遞歸知足2個條件：

1）有反覆執行的過程（調用自身）

2）有跳出反覆執行過程的條件（遞歸出口）

遞歸執行過程當中參數傳遞過程

def f1():
    return "f1" #8. 執行f1()，返回"f1"， f1返回給函數調用者f1()="f1"=>f2()=>f3()=>f4(),最後有ret接受返回值「f1」

def f2():
    r = f1() #6. 執行f2(),獲得 r = f1()
    return r #7. r = f1()， 返回r，即返回執行f1()

def f3(): 
    r = f2() #4. 執行f3(),獲得 r = f2()
    return r #5. r = f2()， 返回r，即返回執行f2()

def f4():     
　　 r = f3() #2.執行f4(),獲得 r = f3()
    return r #3.r = f3()， 返回r，即返回執行f3()

ret = f4() # 1.解釋器讀取函數，把f1,f2,f3,f4的函數存入內存，執行函數f4(), ret接受f4返回值r
print(ret)

def f4(a1, a2):
    print(a1, a2)

    #a1 = 0, a2 = 1,a3 = 1
    #a1 = 1, a2 = 1, a3 = 2
    #a1 = 1, a2 = 2, a3 = 3

    a3 = a1 + a2 #
    f4(a2, a3) #嵌套上面的參數循環執行函數

f4(0, 1)

>>> 
0 1
1 1
1 2
2 3
3 5
5 8
8 13
13 21
21 34
34 55
55 89
...

練習:利用遞歸獲取斐波那契數列中的第 10 個數，並將該值返回給調用者。

def f5(depth, a1, a2): #depth數列的第n個數
　　if depth == 10:
        return a1 #數列第十個數的返回值，最終有啓始的函數'ret'接受
    a3 = a1 + a2
    r = f5(depth +1, a2, a3)
    return r
    
ret = f5(1,0,1)#數值0爲第一個斐波那契的數值 print(ret) >>>
34

裝飾器

裝飾器用於裝飾某個函數或者方法或者類，在調用者調用方式不變的狀況下，能夠在函數執行前或執行後作其餘操做。

裝飾器本質，將原函數封裝到新的函數裏面（），使執行新函數時，既能夠實現新函數的功能，有能夠執行就函數的功能。

def outer(func):#參數func = 以原來的f1函數做爲參數 def inner():#inner函數做爲新的f1函數執行 print("hello")
        r = func()#因爲outer(func)的參數爲f1，此處執行原來的f1函數 print("end")
        return r
    return inner #@outer inner = f1
　　　　　                                                                       
@outer #f1 = outer(f1) 1.執行outer函數，而且將其下面的函數名f1當作參數，func = f1；
　　　　　　　　　　　　　　2.將outer的返回值inner從新賦值給f1，f1=(outer的返回值)=inner, 執行f1() = 執行inner() def f1():
    print("F1")
　　return ooo

def f2():
    print("F2")

def f3():
    print("F3")
"""
.
.
.
"""

def f100():
    print("F100")
　　

f1()

>>>
hello
F1
end
ooo

只要函數應用裝飾器，那麼函數就被從新定義爲：裝飾器的內層函數。

裝飾器裝飾含兩個參數的函數

def outer(func):
    def inner(a1, a2):
        print("123")
        ret = func(a1, a2)
        print("456")
        return ret
    return inner

@outer  #inner = index(a1, a2)，index函數被裝飾到inner函數裏面，
        #執行index函數是須要兩個參數，所以裝飾器函數也須要兩個參數inner(a1,a2)。
        #裝飾器內部執行func() = 執行index(),所以也須要在func函數中加入兩個參數。func(a1, a2)
def index(a1, a2):
    print("執行函數")
    return a1 + a2

ret = index(1, 2)
print(ret)

裝飾器裝飾含N個參數的函數

def f1(*args,**kwargs):#多參數函數
    print(args)
    print(kwargs)

f1(11, 22, 33, 44, 55, 66, 77, 88, k1=123, k2=321)

>>>

　　(11, 22, 33, 44, 55, 66, 77, 88)
　　{'k2': 321, 'k1': 123}

def outer(func):
    def inner(*args, **kwargs):#
        print(args)
        ret = func(*args, **kwargs)#
        print(kwargs)
        return ret
    return inner


@outer
def index(a1, a2, k1=123, k2=456):
    print("執行函數")
    return a1 + a2

ret = index(10, 20, k1=123, k2=456)
print(ret)

>>>
(10, 20)
執行函數
{'k1': 123, 'k2': 456}
30

多個裝飾器裝飾同一個函數

def outer_0(func):
    def inner(*args, **kwargs):
        print("python 3.5")
        ret = func(*args, **kwargs)
        return ret
    return inner

def outer(func):
    def inner(*args, **kwargs):
        print(args)
        ret = func(*args, **kwargs)
        print(kwargs)
        return ret
    return inner

@outer_0
@outer
def index(a1, a2, k1=123, k2=456):
    print("執行函數")
    return a1 + a2

>>>
python 3.5
(10, 20)
執行函數
{'k1': 123, 'k2': 456}
30

多裝飾器嵌套原理

# @outer：  inner = index, outer(func) = outer(index)
# inner = 新的 index 函數 
# index(*args, **kwargs):
#   print(args)
#   ret = index(*args, **kwargs)
#       print("執行函數")
#       return a1 + a2
#   print(kwargs)
#   return ret

#@outer0：inner = 新的 index 函數 + 新的 inner， outer0(func) = outer0(inner(index))
#inner =out0 + index(*args, **kwargs) 函數 +
#index(*args, **kwargs):
#   print("python 3.5")
#   print(args)
#   print("執行函數")
#   return a1 + a2
#   print(kwargs)
#   return ret