repr()函数
当调用repr(object)时，实际调用的是的object.__repr__(self)函数，两者的官方定义如下。
一句话概括就是：repr函数会返回一个字符串，如果有可能的话这个字符串应该是有效的python代码，并且能创建一个这样的对象，如果做不到这一点，也应该返回一个用<>符号包裹的有足够当前对象信息的字符串。
repr(object)
Return a string containing a printable representation of an object. For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to eval(); otherwise, the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information often including the name and address of the object. A class can control what this function returns for its instances by defining a repr() method. If sys.displayhook() is not accessible, this function will raise RuntimeError.
object.__repr__(self)
Called by the repr() built-in function to compute the “official” string representation of an object. If at all possible, this should look like a valid Python expression that could be used to recreate an object with the same value (given an appropriate environment). If this is not possible, a string of the form <...some useful description...> should be returned. The return value must be a string object. If a class defines repr() but not str(), then repr() is also used when an “informal” string representation of instances of that class is required.
This is typically used for debugging, so it is important that the representation is information-rich and unambiguous.
str()函数
当调用str(object)时，实际调用的是object.__str__(self)函数。str函数应该返回言简意赅的对象信息，而不必是有效的python表达式。
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 type(object).str(object), 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.
Passing a bytes object to str() without the encoding or errors arguments falls under the first case of returning the informal string representation (see also the -b command-line option to Python). For example:
>>>str(b'Zoot!')
"b'Zoot!'"
For more information on the str class and its methods, see Text Sequence Type — str and the String Methods section below. To output formatted strings, see the f-strings and Format String Syntax sections. In addition, see the Text Processing Services section.
object.__str__(self)
Called by str(object) and the built-in functions format() and print() to compute the “informal” or nicely printable string representation of an object. The return value must be a string object.
This method differs from object.repr() in that there is no expectation that str() return a valid Python expression: a more convenient or concise representation can be used.
The default implementation defined by the built-in type object calls object.repr().