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75 lines
2.1 KiB
Plaintext
75 lines
2.1 KiB
Plaintext
Content-Type: text/x-zim-wiki
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Wiki-Format: zim 0.4
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Creation-Date: 2012-10-04T13:47:32+08:00
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====== unpack ======
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Created Thursday 04 October 2012
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>>> for k,v in ["fdf",23,"dfdf",33]:
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... print k,v
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...
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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ValueError: __too many__ values to unpack
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顺序容器类型如str, list, tuple__每次迭代时只能返回其中的一个元素__。
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所以第一次返回循环返回**"fdf"**，但是它有三个元素最多只能赋值给两个
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变量。
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>>> for k,v in "dfdf":
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... print k,v
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...
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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ValueError: __need more than 1 value__ to unpack
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字符串迭代时，每次返回其中的一个字符。所以最多只能unpack给一个变量。
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>>> k,v="dfdf"
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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ValueError: __too many values to unpack__
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unpack一个顺序容器类型时，左边变量的数目必须要与容器中元素的个数相同。
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>>> k,v="df"
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>>> print k,v
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d f
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>>>
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In [9]: for k,v in 'dfdf': //对于字符串的迭代，迭代其每次只返回__一个字符__，所以赋值给k,v时出错
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...: print k,v
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...:
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---------------------------------------------------------------------------
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ValueError Traceback (most recent call last)
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<ipython-input-9-5ba17a6181e2> in <module>()
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----> 1 for k,v in 'dfdf':
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2 print k,v
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3
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ValueError: need more than 1 value to unpack
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In [10]: k,v='ff' __//对于可迭代对象，展开后的元素个数必须与等式左边的相等。__
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In [11]: print k,v
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**f f**
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In [13]: k,v='fff'
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---------------------------------------------------------------------------
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ValueError Traceback (most recent call last)
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<ipython-input-13-0aecd2a10b05> in <module>()
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----> 1 k,v='fff'
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ValueError: too many values to unpack
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In [14]:
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In [12]:
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In [12]: for k,v in ['df',[1,2],(3,4)]: __//每次迭代器返回列表中的一个元素，每个元素都可以展开为2个变量。__
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print k,v
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....:
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d f
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1 2
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3 4
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In [13]:
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