函式定義和使用
1、語法
def 函式名(引數): ... 函式體 ... 返回值
函式的定義主要有如下要點：
def：表示函式的關鍵字
函式名：函式的名稱，日後根據函式名呼叫函式
函式體：函式中進行一系列的邏輯計算，如：傳送郵件、計算出 [11,22,38,888,2]中的最大數等...
引數：為函式體提供資料
返回值：當函式執行完畢後，可以給呼叫者返回資料。
2、返回值
函式執行後，將執行結果返回，示例如下：
#!/usr/bin/env python # -*- UTF-8 -*- # Author:Rangle def test(): """ test codes ... """ if 1 == 1: return True else: return False status=test() print(status)
3、引數
python函式的引數分為普通引數、預設引數、動態引數
（1）普通引數
#!/usr/bin/env python # -*- UTF-8 -*- # Author:Rangle def fname(name): print('My name is :%s'%name) fname('Lucy')
（2）預設引數
#!/usr/bin/env python # -*- UTF-8 -*- # Author:Rangle def fname(name,age=18): print('My name is :%s and i\'am %s years old'%(name,age)) fname('Lucy')
（3）動態引數
##接收動態引數，其中動態引數為字串、數字、列表格式，輸出格式為元組
#!/usr/bin/env python # -*- UTF-8 -*- # Author:Rangle def func(*args): print (args) # 執行方式一 func(11,33,4,4454,5) # 執行方式二 li = [11,2,2,3,3,4,54] func(*li)
##接收動態引數，其中引數為字典形式，輸出格式為字典
#!/usr/bin/env python # -*- UTF-8 -*- # Author:Rangle def func(**kwargs): print (kwargs) # 執行方式一 func(name='lucy',age=18) # 執行方式二 li = {'name':'lucy', 'age':18, 'gender':'male'} func(**li)
##接收動態引數，組合形式
def func(*args, **kwargs): print args print kwargs
4、內建函式
官網連結：https://docs.python.org/3/library/functions.html#next
（1）open()函式
用於檔案處理，步驟一般為：開啟檔案——>操作檔案——>關閉檔案
語法如下：
檔案控制程式碼 = open('檔案路徑', '模式')
開啟檔案的模式有：
- r ，只讀模式【預設】
- w，只寫模式【不可讀；不存在則建立；存在則清空內容；】
- x， 只寫模式【不可讀；不存在則建立，存在則報錯】
- a， 追加模式【可讀； 不存在則建立；存在則只追加內容；】
"+" 表示可以同時讀寫某個檔案
- r+， 讀寫【可讀，可寫】
- w+，寫讀【可讀，可寫】
- x+ ，寫讀【可讀，可寫】
- a+， 寫讀【可讀，可寫】
"b"表示以位元組的方式操作
- rb 或 r+b
- wb 或 w+b
- xb 或 w+b
- ab 或 a+b
注：以b方式開啟時，讀取到的內容是位元組型別，寫入時也需要提供位元組型別
class file(object) def close(self): # real signature unknown; restored from __doc__ 關閉檔案 """ 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__ 檔案描述符 """ 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__ 重新整理檔案內部緩衝區 """ flush() -> None. Flush the internal I/O buffer. """ pass def isatty(self): # real signature unknown; restored from __doc__ 判斷檔案是否是同意tty裝置 """ 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__ 獲取下一行資料，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__ 讀取指定位元組資料 """ 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__ 僅讀取一行資料 """ 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__ 讀取所有資料，並根據換行儲存值列表 """ 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__ 指定檔案中指標位置 """ 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__ 獲取當前指標位置 """ tell() -> current file position, an integer (may be a long integer). """ pass def truncate(self, size=None): # real signature unknown; restored from __doc__ 截斷資料，僅保留指定之前資料 """ 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__ 將一個字串列表寫入檔案 """ 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__ 可用於逐行讀取檔案，非全部 """ xreadlines() -> returns self. For backward compatibility. File objects now include the performance optimizations previously implemented in the xreadlines module. """ pass 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 關閉檔案 pass def fileno(self, *args, **kwargs): # real signature unknown 檔案描述符 pass def flush(self, *args, **kwargs): # real signature unknown 重新整理檔案內部緩衝區 pass def isatty(self, *args, **kwargs): # real signature unknown 判斷檔案是否是同意tty裝置 pass def read(self, *args, **kwargs): # real signature unknown 讀取指定位元組資料 pass def readable(self, *args, **kwargs): # real signature unknown 是否可讀 pass def readline(self, *args, **kwargs): # real signature unknown 僅讀取一行資料 pass def seek(self, *args, **kwargs): # real signature unknown 指定檔案中指標位置 pass def seekable(self, *args, **kwargs): # real signature unknown 指標是否可操作 pass def tell(self, *args, **kwargs): # real signature unknown 獲取指標位置 pass def truncate(self, *args, **kwargs): # real signature unknown 截斷資料，僅保留指定之前資料 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
（2）檔案操作之管理上下文
通過Open()函式，需要顯示關閉，這種可能容易導致忽略關閉檔案。通過with open() as f 管理上下文可以自動關閉檔案，具體語法如下：
with open('log','r') as f: ...
其中2.7以後支援開啟多個檔案
with open('log1') as obj1, open('log2') as obj2: pass
（3）三元運算
如果1==1為true則返回name='Lucy'，否則則返回name='Tom'
name = 'Lucy' if 1 == 1 else 'Tom'
（4）判斷函式
s='abc'
s.isalnum() 所有字元都是數字或者字母，為真返回 Ture，否則返回 False。
s.isalpha() 所有字元都是字母，為真返回 Ture，否則返回 False。
s.isdigit() 所有字元都是數字，為真返回 Ture，否則返回 False。
s.islower() 所有字元都是小寫，為真返回 Ture，否則返回 False。
s.isupper() 所有字元都是大寫，為真返回 Ture，否則返回 False。
s.istitle() 所有單詞都是首字母大寫，為真返回 Ture，否則返回 False。
s.isspace() 所有字元都是空白字元，為真返回 Ture，否則返回 False。
（5）格式輸出
格式符號如下： %s 字串 (採用str()的顯示) %r 字串 (採用repr()的顯示) %c 單個字元 %b 二進位制整數 %d 十進位制整數 %i 十進位制整數 %o 八進位制整數 %x 十六進位制整數 %e 指數 (基底寫為e) %E 指數 (基底寫為E) %f 浮點數 %F 浮點數，與上相同 %g 指數(e)或浮點數 (根據顯示長度) %G 指數(E)或浮點數 (根據顯示長度) %% 字元"%" 主要說明： %s:格式化初始字串 %d:格式化輸出整數數字 %f:格式化輸出浮點數,其中可以通過%.nf保留n位小數，n位實際數字。例如保留兩位小數%.2f %8d:指定輸出數字佔用8個字元位置，其中輸出數字居右排列 %-8d:指定輸出數字佔用8個字元位置，其中輸出數字居左排列 %08d:指定佔位符號用0表示 format(0.0015,'.2e'):科學計數法表示1.50e-03即1.50*10^-3
5、練習題
（1）、簡述普通引數、指定引數、預設引數、動態引數的區別 （2）、寫函式，計算傳入字串中【數字】、【字母】、【空格] 以及 【其他】的個數 （3）、寫函式，判斷使用者傳入的物件（字串、列表、元組）長度是否大於5。 （4）、寫函式，檢查使用者傳入的物件（字串、列表、元組）的每一個元素是否含有空內容。 （5）、寫函式，檢查傳入列表的長度，如果大於2，那麼僅保留前兩個長度的內容，並將新內容返回給呼叫者。 （6）、寫函式，檢查獲取傳入列表或元組物件的所有奇數位索引對應的元素，並將其作為新列表返回給呼叫者。 （7）、寫函式，檢查傳入字典的每一個value的長度,如果大於2，那麼僅保留前兩個長度的內容，並將新內容返回給呼叫者。 1 2 3 dic = {"k1": "v1v1", "k2": [11,22,33,44]} PS:字典中的value只能是字串或列表 （8）、寫函式，利用遞迴獲取斐波那契數列中的第 10 個數，並將該值返回給呼叫者。