[英]In Python, why does this line run from the file (without exception), but throw an exception when run in the shell?
我正在瀏覽Peter Norvig的Sudoku求解器代碼( http://norvig.com/sudopy.shtml ),並且遇到了這一行:
peers = dict((s, set(sum(units[s],[]))-set([s]))
for s in squares)
如果我將代碼復制到並包含此行(即直到第28行),並從文件中運行它,它運行正常,字典'peers'具有例外值。 但是,如果在我運行此文件后,我嘗試從shell運行此行,我收到一個錯誤:
peers = dict((s, set(sum(units[s],[]))-set([s]))
for s in squares)
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-33-2652de1ecd8a> in <module>()
1 peers = dict((s, set(sum(units[s],[]))-set([s]))
----> 2 for s in squares)
<ipython-input-33-2652de1ecd8a> in <genexpr>((s,))
1 peers = dict((s, set(sum(units[s],[]))-set([s]))
----> 2 for s in squares)
C:\PyCanopy\User\lib\site-packages\numpy\core\fromnumeric.pyc in sum(a, axis, dtype, out, keepdims)
1717 except AttributeError:
1718 return _methods._sum(a, axis=axis, dtype=dtype,
-> 1719 out=out, keepdims=keepdims)
1720 # NOTE: Dropping the keepdims parameters here...
1721 return sum(axis=axis, dtype=dtype, out=out)
C:\PyCanopy\User\lib\site-packages\numpy\core\_methods.pyc in _sum(a, axis, dtype, out, keepdims)
30
31 def _sum(a, axis=None, dtype=None, out=None, keepdims=False):
---> 32 return umr_sum(a, axis, dtype, out, keepdims)
33
34 def _prod(a, axis=None, dtype=None, out=None, keepdims=False):
TypeError: cannot perform reduce with flexible type
我無法弄清楚為什么會這樣。 我發現這行代碼開頭很奇怪,因為它有一個dict
鍵值和空[]
的sum
。 任何指導? 謝謝。
代碼在python
解釋器和ipython
都適用於我。 看起來在運行代碼之前你做了這個:
from numpy import sum
所以現在sum
不是python的標准sum
,但它是從numpy
導入的不同函數。 這就是代碼引發錯誤的原因。
解決方案:從ipython
shell退出,再次運行並將代碼粘貼到其中。
編輯 :關於空列表的總和,這只是使單位平坦的技巧。 例如,單位['I1']如下所示:
[['A1', 'B1', 'C1', 'D1', 'E1', 'F1', 'G1', 'H1', 'I1'],
['I1', 'I2', 'I3', 'I4', 'I5', 'I6', 'I7', 'I8', 'I9'],
['G1', 'G2', 'G3', 'H1', 'H2', 'H3', 'I1', 'I2', 'I3']]
sum(units['I1'], [])
如下所示:
['A1', 'B1', 'C1', 'D1', 'E1', 'F1', 'G1', 'H1', 'I1', 'I1', 'I2', 'I3', 'I4', 'I5', 'I6', 'I7', 'I8', 'I9', 'G1', 'G2', 'G3', 'H1', 'H2', 'H3', 'I1', 'I2', 'I3']
引擎蓋下的總和是這樣的:
list = []
for elem in units['I1']:
list = list + elem
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