Python内置函数(61)——str

英文文档：

class str(object='') class

str(object=b'', encoding='utf-8', errors='strict')

Return a string version of object. If object is not provided, returns the empty string. Otherwise, the behavior of str() depends on whether encoding or errors is given, as follows.

If neither encoding nor errors is given, str(object) returns object.__str__(), which is the “informal” or nicely printable string representation of object. For string objects, this is the string itself. If object does not have a __str__() method, then str() falls back to returning repr(object).

If at least one of encoding or errors is given, object should be a bytes-like object (e.g. bytes or bytearray). In this case, if object is a bytes (or bytearray) object, then str(bytes, encoding, errors) is equivalent to bytes.decode(encoding, errors). Otherwise, the bytes object underlying the buffer object is obtained before calling bytes.decode(). See Binary Sequence Types — bytes, bytearray, memoryview and Buffer Protocol for information on buffer objects.

说明：

　　1. str函数功能时将对象转换成其字符串表现形式，如果不传入参数，将返回空字符串。

>>> str()
''
>>> str(None)
'None'
>>> str('abc')
'abc'
>>> str(123)
''

　　2. 当转换二进制流时，可以传入参数encoding，表示读取字节数组所使用的编码格式；参数errors，表示读取二进制的错误级别。(这两个参数和open方法中的同名参数有相同取值和类似的含义，详见Python内置函数(47)——open)。

>>> file = open('test.txt','rb') # 打开文件
>>> fileBytes = file.read() # 读取二进制流
>>> fileBytes
b'\xe6\x88\x91\xe6\x98\xaf\xe7\xac\xac1\xe8\xa1\x8c\xe6\x96\x87\xe6\x9c\xac\xef\xbc\x8c\xe6\x88\x91\xe5\xb0\x86\xe8\xa2\xab\xe6\x98\xbe\xe7\xa4\xba\xe5\x9c\xa8\xe5\xb1\x8f\xe5\xb9\x95\r\n\xe6\x88\x91\xe6\x98\xaf\xe7\xac\xac2\xe8\xa1\x8c\xe6\x96\x87\xe6\x9c\xac\xef\xbc\x8c\xe6\x88\x91\xe5\xb0\x86\xe8\xa2\xab\xe6\x98\xbe\xe7\xa4\xba\xe5\x9c\xa8\xe5\xb1\x8f\xe5\xb9\x95\r\n\xe6\x88\x91\xe6\x98\xaf\xe7\xac\xac3\xe8\xa1\x8c\xe6\x96\x87\xe6\x9c\xac\xef\xbc\x8cr\xe6\x88\x91\xe5\xb0\x86\xe8\xa2\xab\xe6\x98\xbe\xe7\xa4\xba\xe5\x9c\xa8\xe5\xb1\x8f\xe5\xb9\x95'
>>> str(fileBytes) # 默认将二进制流转换成字符串表现形式
"b'\\xe6\\x88\\x91\\xe6\\x98\\xaf\\xe7\\xac\\xac1\\xe8\\xa1\\x8c\\xe6\\x96\\x87\\xe6\\x9c\\xac\\xef\\xbc\\x8c\\xe6\\x88\\x91\\xe5\\xb0\\x86\\xe8\\xa2\\xab\\xe6\\x98\\xbe\\xe7\\xa4\\xba\\xe5\\x9c\\xa8\\xe5\\xb1\\x8f\\xe5\\xb9\\x95\\r\\n\\xe6\\x88\\x91\\xe6\\x98\\xaf\\xe7\\xac\\xac2\\xe8\\xa1\\x8c\\xe6\\x96\\x87\\xe6\\x9c\\xac\\xef\\xbc\\x8c\\xe6\\x88\\x91\\xe5\\xb0\\x86\\xe8\\xa2\\xab\\xe6\\x98\\xbe\\xe7\\xa4\\xba\\xe5\\x9c\\xa8\\xe5\\xb1\\x8f\\xe5\\xb9\\x95\\r\\n\\xe6\\x88\\x91\\xe6\\x98\\xaf\\xe7\\xac\\xac3\\xe8\\xa1\\x8c\\xe6\\x96\\x87\\xe6\\x9c\\xac\\xef\\xbc\\x8cr\\xe6\\x88\\x91\\xe5\\xb0\\x86\\xe8\\xa2\\xab\\xe6\\x98\\xbe\\xe7\\xa4\\xba\\xe5\\x9c\\xa8\\xe5\\xb1\\x8f\\xe5\\xb9\\x95'"
>>> str(fileBytes,'utf-8') # 传入encoding参数，函数将以此编码读取二进制流的内容
'我是第1行文本，我将被显示在屏幕\r\n我是第2行文本，我将被显示在屏幕\r\n我是第3行文本，r我将被显示在屏幕'
>>> str(fileBytes,'gbk') # 当传入encoding不能解码时，会报错(即errors参数默认为strict)
Traceback (most recent call last):
  File "<pyshell#46>", line 1, in <module>
    str(fileBytes,'gbk')
UnicodeDecodeError: 'gbk' codec can't decode byte 0xac in position 8: illegal multibyte sequence
>>> str(fileBytes,'gbk','ignore') # 'ignore' 忽略级别，字符编码有错，忽略掉.
'鎴戞槸绗1琛屾枃鏈锛屾垜灏嗚鏄剧ず鍦ㄥ睆骞\r\n鎴戞槸绗2琛屾枃鏈锛屾垜灏嗚鏄剧ず鍦ㄥ睆骞\r\n鎴戞槸绗3琛屾枃鏈锛宺鎴戝皢琚鏄剧ず鍦ㄥ睆骞'
>>> str(fileBytes,'gbk','replace') # 'replace' 替换级别，字符编码有错的，替换成？.
'鎴戞槸绗�1琛屾枃鏈�锛屾垜灏嗚��鏄剧ず鍦ㄥ睆骞�\r\n鎴戞槸绗�2琛屾枃鏈�锛屾垜灏嗚��鏄剧ず鍦ㄥ睆骞�\r\n鎴戞槸绗�3琛屾枃鏈�锛宺鎴戝皢琚�鏄剧ず鍦ㄥ睆骞�'