blocks|key|145694|text|enumerate()+function向迭代器添加一个计数器。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|145695|因此，对于cursor中的每个元素，使用(counter,+element)生成一个元组；for循环分别将该元组绑定到row_number和row。|145696|演示：|145697|>>>+elements+=+('foo',+'bar',+'baz')
>>>+for+elem+in+elements:
...+++++print+elem
...+
foo
bar
baz
>>>+for+count,+elem+in+enumerate(elements):
...+++++print+count,+elem
...+
0+foo
1+bar
2+baz|code-block|syntax|javascript|145698|默认情况下，enumerate()从0开始计数，但如果您给它第二个整数参数，它将从该数字开始计数：|145699|>>>+for+count,+elem+in+enumerate(elements,+42):
...+++++print+count,+elem
...+
42+foo
43+bar
44+baz|145700|如果要用Python语言重新实现enumerate()，有两种方法可以实现；一种是使用itertools.count()进行计数，另一种是在generator+function中手动计数|145701|from+itertools+import+count

def+enumerate(it,+start=0):
++++#+return+an+iterator+that+adds+a+counter+to+each+element+of+it
++++return+zip(count(start),+it)|145702|和|145703|def+enumerate(it,+start=0):
++++count+=+start
++++for+elem+in+it:
++++++++yield+(count,+elem)
++++++++count+%2B=+1|145704|Python更接近后者，优化后的方法是在常见的for+i,+...解包情况下重用单个元组对象，并对计数器使用标准的C整数值，直到计数器变得太大而不能避免使用Python整数对象(它是无界的)。|145705|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/2/library/functions.html#enumerate|1|https://docs.python.org/3/library/itertools.html#itertools.count|2|https://stackoverflow.com/questions/231767/what-does-the-yield-keyword-do^0|0|B|0|K|0|0|5|6|K|I|19|3|1N|A|1Y|3|0|0|0|6|B|I|1|0|0|G|B|17|H|17|H|1|1Y|I|2|0|0|0|0|N|A|0^^$0|@$1|2|3|4|5|6|7|1E|8|@$9|1F|A|1G|B|C]]|D|@$9|1H|A|1I|1|1J]]|E|$]]|$1|F|3|G|5|6|7|1K|8|@$9|1L|A|1M|B|C]|$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1V|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1W|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1X|8|@$9|1Y|A|1Z|B|C]|$9|20|A|21|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|L|7|22|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|23|8|@$9|24|A|25|B|C]|$9|26|A|27|B|C]]|D|@$9|28|A|29|1|2A]|$9|2B|A|2C|1|2D]]|E|$]]|$1|U|3|V|5|L|7|2E|8|@]|D|@]|E|$M|N]]|$1|W|3|X|5|6|7|2F|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|L|7|2G|8|@]|D|@]|E|$M|N]]|$1|10|3|11|5|6|7|2H|8|@$9|2I|A|2J|B|C]]|D|@]|E|$]]|$1|12|3|-4|5|6|7|2K|8|@]|D|@]|E|$]]]|13|$14|$5|15|16|17|E|$18|19]]|1A|$5|15|16|17|E|$18|1B]]|1C|$5|15|16|17|E|$18|1D]]]]

The <a href="http://docs.python.org/2/library/functions.html#enumerate" rel="noreferrer"><code>enumerate()</code> function</a> adds a counter to an iterable.

So for each element in <code>cursor</code>, a tuple is produced with <code>(counter, element)</code>; the <code>for</code> loop binds that to <code>row_number</code> and <code>row</code>, respectively.

Demo:

<pre><code>&gt;&gt;&gt; elements = ('foo', 'bar', 'baz')
&gt;&gt;&gt; for elem in elements:
... print elem
... 
foo
bar
baz
&gt;&gt;&gt; for count, elem in enumerate(elements):
... print count, elem
... 
0 foo
1 bar
2 baz
</code></pre>

By default, <code>enumerate()</code> starts counting at <code>0</code> but if you give it a second integer argument, it'll start from that number instead:

<pre><code>&gt;&gt;&gt; for count, elem in enumerate(elements, 42):
... print count, elem
... 
42 foo
43 bar
44 baz
</code></pre>

If you were to re-implement <code>enumerate()</code> in Python, here are two ways of achieving that; one using <a href="https://docs.python.org/3/library/itertools.html#itertools.count" rel="noreferrer"><code>itertools.count()</code></a> to do the counting, the other manually counting in a <a href="https://stackoverflow.com/questions/231767/what-does-the-yield-keyword-do">generator function</a>:

<pre><code>from itertools import count

def enumerate(it, start=0):
 # return an iterator that adds a counter to each element of it
 return zip(count(start), it)
</code></pre>

and

<pre><code>def enumerate(it, start=0):
 count = start
 for elem in it:
 yield (count, elem)
 count += 1
</code></pre>

The <a href="https://github.com/python/cpython/blob/master/Objects/enumobject.c" rel="noreferrer">actual implementation in C</a> is closer to the latter, with optimisations to reuse a single tuple object for the common <code>for i, ...</code> unpacking case and using a standard C integer value for the counter until the counter becomes too large to avoid using a Python integer object (which is unbounded).

blocks|key|4652334|text|它是一个内置函数，返回一个可以迭代的对象。参见the+documentation。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4652335|简而言之，它循环遍历可迭代对象(如列表)的元素，以及组合在元组中的索引号：|4652336|for+item+in+enumerate(["a",+"b",+"c"]):
++++print+item|code-block|syntax|javascript|4652337|打印|4652338|(0,+"a")
(1,+"b")
(2,+"c")|4652339|如果你想循环遍历一个序列(或其他可迭代的东西)，并且想要有一个可用的索引计数器，这是很有帮助的。如果您希望计数器从其他值(通常为1)开始，则可以将该值作为第二个参数提供给enumerate。|style|CODE|4652340|entityMap|0|LINK|mutability|MUTABLE|url|http://docs.python.org/2/library/functions.html#enumerate^0|N|H|0|0|0|0|0|0|2D|9|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|15|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|17|8|@]|9|@]|C|$I|J]]|$1|O|3|P|5|6|7|18|8|@$A|19|B|1A|Q|R]]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

It's a builtin function that returns an object that can be iterated over. See <a href="http://docs.python.org/2/library/functions.html#enumerate" rel="noreferrer">the documentation</a>.

In short, it loops over the elements of an iterable (like a list), as well as an index number, combined in a tuple:

<pre><code>for item in enumerate(["a", "b", "c"]):
 print item
</code></pre>

prints

<pre><code>(0, "a")
(1, "b")
(2, "c")
</code></pre>

It's helpful if you want to loop over a sequence (or other iterable thing), and also want to have an index counter available. If you want the counter to start from some other value (usually 1), you can give that as second argument to <code>enumerate</code>.

blocks|key|4652355|text|枚举函数的工作方式如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4652356|doc+=+"""I+like+movie.+But+I+don't+like+the+cast.+The+story+is+very+nice"""
doc1+=+doc.split('.')
for+i+in+enumerate(doc1):
+++++print(i)|code-block|syntax|javascript|4652357|输出为|4652358|(0,+'I+like+movie')
(1,+"+But+I+don't+like+the+cast")
(2,+'+The+story+is+very+nice')|4652359|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The enumerate function works as follows:

<pre><code>doc = """I like movie. But I don't like the cast. The story is very nice"""
doc1 = doc.split('.')
for i in enumerate(doc1):
 print(i)
</code></pre>

The output is

<pre><code>(0, 'I like movie')
(1, " But I don't like the cast")
(2, ' The story is very nice')
</code></pre>

blocks|key|4652393|text|我假设你知道如何迭代一些列表中的元素：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4652394|for+el+in+my_list:
++++#+do+something|code-block|syntax|javascript|4652395|现在，有时您不仅需要迭代元素，还需要每次迭代的索引。一种方法是：|4652396|i+=+0
for+el+in+my_list:
++++#+do+somethings,+and+use+value+of+"i"+somehow
++++i+%2B=+1|4652397|然而，更好的方法是使用函数"enumerate“。enumerate所做的是接收一个列表，并返回一个类似列表的对象(一个可以遍历的可迭代对象)，但是这个新列表本身的每个元素都包含两个元素:索引和来自原始输入列表的值:所以如果您有|4652398|arr+=+['a',+'b',+'c']|4652399|然后，命令enumerate(arr)将返回类似以下内容：|offset|length|style|CODE|4652400|[(0,'a'),+(1,'b'),+(2,'c')]|4652401|现在，如果您遍历一个列表(或可迭代元素)，其中每个元素本身都有两个子元素，则可以在for循环中捕获这两个子元素，如下所示：|4652402|for+index,+value+in+enumerate(arr):
++++print(index,value)|4652403|它将打印出enumerate的输出的子元素。|4652404|一般来说，你基本上可以将列表中的多个项目“解包”成多个变量，如下所示：|4652405|idx,value+=+(2,'c')
print(idx)
print(value)|4652406|它将打印|4652407|2
c|4652408|这是在该循环的每次迭代中发生的赋值类型，其中enumerate(arr)是可迭代的。|4652409|entityMap^0|0|0|0|0|0|0|5|E|0|0|15|3|0|0|0|0|0|0|0|M|E|0^^$0|@$1|2|3|4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1F|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|1G|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1I|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|1J|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|1K|8|@$Q|1L|R|1M|S|T]]|9|@]|A|$]]|$1|U|3|V|5|D|7|1N|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1O|8|@$Q|1P|R|1Q|S|T]]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|1R|8|@]|9|@]|A|$E|F]]|$1|10|3|11|5|6|7|1S|8|@]|9|@]|A|$]]|$1|12|3|13|5|6|7|1T|8|@]|9|@]|A|$]]|$1|14|3|15|5|D|7|1U|8|@]|9|@]|A|$E|F]]|$1|16|3|17|5|6|7|1V|8|@]|9|@]|A|$]]|$1|18|3|19|5|D|7|1W|8|@]|9|@]|A|$E|F]]|$1|1A|3|1B|5|6|7|1X|8|@$Q|1Y|R|1Z|S|T]]|9|@]|A|$]]|$1|1C|3|-4|5|6|7|20|8|@]|9|@]|A|$]]]|1D|$]]

I am assuming that you know how to iterate over elements in some list:
<pre><code>for el in my_list:
 # do something
</code></pre>
Now sometimes not only you need to iterate over the elements, but also you need the index for each iteration. One way to do it is:
<pre><code>i = 0
for el in my_list:
 # do somethings, and use value of &quot;i&quot; somehow
 i += 1
</code></pre>
However, a nicer way is to user the function &quot;enumerate&quot;. What enumerate does is that it receives a list, and it returns a list-like object (an iterable that you can iterate over) but each element of this new list itself contains 2 elements: the index and the value from that original input list:
So if you have
<pre><code>arr = ['a', 'b', 'c']
</code></pre>
Then the command
<code>enumerate(arr)</code>
returns something like:
<pre><code>[(0,'a'), (1,'b'), (2,'c')]
</code></pre>
Now If you iterate over a list (or an iterable) where each element itself has 2 sub-elements, you can capture both of those sub-elements in the <code>for</code> loop like below:
<pre><code>for index, value in enumerate(arr):
 print(index,value)
</code></pre>
which would print out the sub-elements of the output of enumerate.
And in general you can basically &quot;unpack&quot; multiple items from list into multiple variables like below:
<pre><code>idx,value = (2,'c')
print(idx)
print(value)
</code></pre>
which would print
<pre><code>2
c
</code></pre>
This is the kind of assignment happening in each iteration of that loop with <code>enumerate(arr)</code> as iterable.

What does <code>for row_number, row in enumerate(cursor):</code> do in Python?

What does <code>enumerate</code> mean in this context?

What does enumerate() mean?

Python

for row_number, row in enumerate(cursor):在Python中做什么？在这种情况下，enumerate是什么意思？

问enumerate()是什么意思？
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