2019年4月21日 · The enumerate() function adds a counter to an iterable.. So for each element in cursor, a tuple is produced with (counter, element); the for loop binds that to row_number and row, respectively.

Use the Enumerate Function. Python's enumerate function reduces the visual clutter by hiding the accounting for the indexes, and encapsulating the iterable into another iterable (an enumerate object) that yields a two-item tuple of the index and the item that the original iterable would provide. That looks like this:

2015年11月25日 · I've been told that there's an enumerate() function that can take care of the "i" variable for me: for i, l in enumerate(['a', 'b', 'c']): print "%d: %s" % (i, l) However, I can't figure out how to combine the two: How do I use enumerate when the list in question is made of tuples?

2015年7月1日 · The enumerate-function returns an iterator. The concept of an iterator is described here.. Basically this means that the iterator gets initialized pointing to the first item of the list and then returning the next element of the list every time its next() method gets called.

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2014年5月15日 · Very interesting. Just to be sure I've got this straight, iterators (or iterables) are defined by their behavior, whereas there are actual "generator" and "enumerate" classes that define those objects. "enumerate"-class objects share many behaviors with "generator"-class objects, but so do objects of many other classes.

2014年2月11日 · for i,row in itertools.takewhile(lambda (i,val):i < limit,enumerate(myiterable[2:],2)): to rephrase the other suggestion (note that it will only work if your iterable is a sliceable object) start,stop = 11,20 my_items = range(100) for i,row in enumerate(my_items[start:stop],start): ....

2012年8月16日 · In Python 2.x, use xrange instead of range, because xrange uses less memory, because it doesn't create a temporary list. In Python 3.x, there is only range, which is the less-memory version. Thus, in Python 2.x, iterating over a range(n) uses O(n) memory temporarily, and iterating over an xrange(n) uses O(1) memory temporarily.

Edit 2: as pointed out in the comments to this question, this is not entirely equivalent. While it produces the same values as Python's enumerate, it doesn't do so in the same generative fashion that Python's enumerate does. Thus for large collections this approach could be quite prohibitive.

2015年3月21日 · The issue is not enumerate, and neither the start argument, but the fact that when you do start=1, you're enumerating from 1 to valueList+1: