先看一下python2中的map函数：
def map(function, sequence, *sequence_1): # real signature unknown; restored from __doc__
"""
map(function, sequence[, sequence, ...]) -> list
Return a list of the results of applying the function to the items of
the argument sequence(s). If more than one sequence is given, the
function is called with an argument list consisting of the corresponding
item of each sequence, substituting None for missing values when not all
sequences have the same length. If the function is None, return a list of
the items of the sequence (or a list of tuples if more than one sequence).
"""
return []也即是将一个function作用于sequence中每个元素身上，最后返回这个被function作用后的list。
再看一下python3中的map函数：
class map(object):
"""
map(func, *iterables) --> map object
Make an iterator that computes the function using arguments from
each of the iterables. Stops when the shortest iterable is exhausted.
"""
def __getattribute__(self, *args, **kwargs): # real signature unknown
""" Return getattr(self, name). """
pass
def __init__(self, func, *iterables): # real signature unknown; restored from __doc__
pass
def __iter__(self, *args, **kwargs): # real signature unknown
""" Implement iter(self). """
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 __reduce__(self, *args, **kwargs): # real signature unknown
""" Return state information for pickling. """
pass
在python3中map被封装成了一个类，功能依旧是将function作用于要被遍历的序列，但是最后返回的结果就是一个对象了。
通过代码举一个将int转换为float的例子：
if __name__ == '__main__':
x = [1, 2, 3, 4, 5]
y = map(float, x)
print(y)python2中：
[1.0, 2.0, 3.0, 4.0, 5.0]python3中：
<map object at 0x000001FB6DAF0A58>
如何将python3中的对象转换为python2中的形式呢？
只需要通过list作用于map即可：
if __name__ == '__main__':
x = [1, 2, 3, 4, 5]
y = list(map(float, x))
print(y)[1.0, 2.0, 3.0, 4.0, 5.0]