python2, python3 的map函数

网上找了段代码:

# 加载数据
def loadDataSet(fileName):  # 解析文件，按tab分割字段，得到一个浮点数字类型的矩阵
    dataMat = []              # 文件的最后一个字段是类别标签
    fr = open(fileName)
    for line in fr.readlines():
        curLine = line.strip().split('\t')
        fltLine = map(float, curLine)    # 将每个元素转成float类型
        dataMat.append(fltLine)
    return dataMat
#...
# 构建聚簇中心，取k个(此例中为4)随机质心
def randCent(dataSet, k):
    n = shape(dataSet)[1]
    centroids = mat(zeros((k,n)))   # 每个质心有n个坐标值，总共要k个质心
    for j in range(n):
        minJ = min(dataSet[:,j])
        maxJ = max(dataSet[:,j])
        rangeJ = float(maxJ - minJ)
        centroids[:,j] = minJ + rangeJ * random.rand(k, 1)
    return centroids

 在python3.7下报错:

 

(ludwig.py37) e:\test\kmeans>python km0.py
Traceback (most recent call last):
  File "km0.py", line 54, in <module>
  File "km0.py", line 34, in kMeans
  File "km0.py", line 25, in randCent
TypeError: unsupported operand type(s) for -: 'map' and 'map'

 

在python2.7下正常

 

在python3.7和python2.7下print了加载完的数据集dataMat中的一条数据,得到了不同的结果:

python3.7:

(ludwig.py37) e:\test\kmeans>python km.py
<map object at 0x000000001343A550>

 

 python2.7:

(ocr.py27) e:\test\kmeans>python km0.py
[1.658985, 4.285136]

 

 3.7返回的是map对象;2.7返回的是list对象;

 

 感觉是map()函数在python版本下的差异导致,验证一下:

python3.7:

 

(ludwig.py37) e:\test\kmeans>python
Python 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:59:51) [MSC v.1914 64 bit (AMD6
4)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> map
<class 'map'>

  

python2.7:

(ocr.py27) e:\test\kmeans>python
Python 2.7 (r27:82525, Jul  4 2010, 07:43:08) [MSC v.1500 64 bit (AMD64)] on win
32
Type "help", "copyright", "credits" or "license" for more information.
>>> map
<built-in function map>

 

印证猜测:

python2下map是一个build-in function; python3下map是一个class,map()返回的是一个map class对象;

 

修改代码将map返回的结果强制转一下list即可支持python2, python3:

 

# 加载数据
def loadDataSet(fileName):  # 解析文件，按tab分割字段，得到一个浮点数字类型的矩阵
    dataMat = []              # 文件的最后一个字段是类别标签
    fr = open(fileName)
    for line in fr.readlines():
        curLine = line.strip().split('\t')
        fltLine = map(float, curLine)    # 将每个元素转成float类型
        fltLine = list(fltLine) #!!!!python3中 map返回的不是list是map类,形如<map at 0x3fed1d0>
        dataMat.append(fltLine)
    return dataMat

 

 python2.7, python3.7下都可通过.

评论

1 楼 kissmett 2019-05-30  

filter函数亦同