python-3.x - python 3.5 错误 : can't add `map` results together

Question

我有一段使用 python 2.7 的代码，我正在尝试转换它，以便我可以将它与 python 3.5 一起使用，但由于映射，我在流动代码中遇到错误。解决这个问题的最佳方法是什么？

文件“/Users/newbie/anaconda3/lib/python3.5/site-packages/keras/caffe/caffe_utils.py”，第 74 行，parse_network blobs = top_blobs + bottom_blobs

TypeError: + 不支持的操作数类型: 'ma​​p' 和 'ma​​p'

 def parse_network(layers, phase):
 '''
    Construct a network from the layers by making all blobs and  layers(operations) as nodes.
'''
  nb_layers = len(layers)
  network = {}

   for l in range(nb_layers):
     included = False
     try:
        # try to see if the layer is phase specific
        if layers[l].include[0].phase == phase:
            included = True
     except IndexError:
        included = True

     if included:
        layer_key = 'caffe_layer_' + str(l)  # actual layers, special annotation to mark them
        if layer_key not in network:
            network[layer_key] = []
        top_blobs = map(str, layers[l].top)
        bottom_blobs = map(str, layers[l].bottom)
        blobs = top_blobs + bottom_blobs

        for blob in blobs:
            if blob not in network:
                network[blob] = []
        for blob in bottom_blobs:
            network[blob].append(layer_key)
        for blob in top_blobs:
                network[layer_key].append(blob)
 network = acyclic(network)  # Convert it to be truly acyclic
 network = merge_layer_blob(network)  # eliminate 'blobs', just have layers
 return network

Answer 1

Python 3 中的

map 返回一个迭代器，而 Python 2 中的 map 返回一个列表:

python 2:

>>> type(map(abs, [1, -2, 3, -4]))
<type 'list'>

python 3:

>>> type(map(abs, [1, -2, 3, -4]))
<class 'map'>

(请注意，map 更加特殊，但它肯定不是 list。)

您不能简单地添加迭代器。但是您可以使用 itertools.chain 链接它们:

>>> from itertools import chain
>>> chain(map(abs, [1, -2, 3, -4]), map(abs, [5, -6, 7, -8]))
<itertools.chain object at 0x7fe0dc0775f8>

对于最终结果，您要么必须遍历链，要么对其求值:

>>> for value in chain(map(abs, [1, -2, 3, -4]), map(abs, [5, -6, 7, -8])):
...     print(value)
... 
1
2
3
4
5
6
7
8

或

>>> list(chain(map(abs, [1, -2, 3, -4]), map(abs, [5, -6, 7, -8])))
[1, 2, 3, 4, 5, 6, 7, 8]

请注意，前者更自然，除非绝对必要，否则应避免将迭代器作为最后一个示例进行评估:它可以节省内存和可能的计算能力(例如，在循环中有中断的地方，以便进一步值不必评估)。