问题:如何枚举从1开始的数字范围

我正在使用Python 2.5,我想要这样的枚举(从1而不是0开始):

[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

我知道在python 2.6中可以执行以下操作:h = enumerate(range(2000,2005),1)给出上述结果,但是在python2.5中您不能…

使用python2.5:

>>> h = enumerate(range(2000, 2005))
>>> [x for x in h]
[(0, 2000), (1, 2001), (2, 2002), (3, 2003), (4, 2004)]

有谁知道在python 2.5中获得理想结果的方法?

谢谢,

杰夫

I am using Python 2.5, I want an enumeration like so (starting at 1 instead of 0):

[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

I know in Python 2.6 you can do: h = enumerate(range(2000, 2005), 1) to give the above result but in python2.5 you cannot…

Using python2.5:

>>> h = enumerate(range(2000, 2005))
>>> [x for x in h]
[(0, 2000), (1, 2001), (2, 2002), (3, 2003), (4, 2004)]

Does anyone know a way to get that desired result in python 2.5?

Thanks,

Jeff


回答 0

正如您已经提到的,在Python 2.6或更高版本中,这很容易做到:

enumerate(range(2000, 2005), 1)

Python 2.5及更早版本不支持该start参数,因此您可以创建两个范围对象并将其压缩:

r = xrange(2000, 2005)
r2 = xrange(1, len(r) + 1)
h = zip(r2, r)
print h

结果:

[(1,2000),(2,2001),(3,2002),(4,2003),(5,2004)]

如果要创建生成器而不是列表,则可以使用izip

As you already mentioned, this is straightforward to do in Python 2.6 or newer:

enumerate(range(2000, 2005), 1)

Python 2.5 and older do not support the start parameter so instead you could create two range objects and zip them:

r = xrange(2000, 2005)
r2 = xrange(1, len(r) + 1)
h = zip(r2, r)
print h

Result:

[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

If you want to create a generator instead of a list then you can use izip instead.


回答 1

只是为了后代而已,在2.6中添加了“ start”参数来进行枚举,如下所示:

enumerate(sequence, start=1)

Just to put this here for posterity sake, in 2.6 the “start” parameter was added to enumerate like so:

enumerate(sequence, start=1)


回答 2

简单,只需定义您自己的函数即可执行您想要的操作:

def enum(seq, start=0):
    for i, x in enumerate(seq):
        yield i+start, x

Easy, just define your own function that does what you want:

def enum(seq, start=0):
    for i, x in enumerate(seq):
        yield i+start, x

回答 3

Python 3

官方文件: enumerate(iterable, start=0)

所以您可以这样使用它:

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']

>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

Python 3

Official documentation: enumerate(iterable, start=0)

So you would use it like this:

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']

>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

回答 4

在Python 2.5中执行查询的最简单方法就是:

import itertools as it

... it.izip(it.count(1), xrange(2000, 2005)) ...

如果您想要一个列表(看起来像),请使用zip代替it.izip

(顺便说一句,顺便说一句,从生成器或任何其他可迭代X生成列表的最佳方法不是 [x for x in X],而是list(X)。)

Simplest way to do in Python 2.5 exactly what you ask about:

import itertools as it

... it.izip(it.count(1), xrange(2000, 2005)) ...

If you want a list, as you appear to, use zip in lieu of it.izip.

(BTW, as a general rule, the best way to make a list out of a generator or any other iterable X is not [x for x in X], but rather list(X)).


回答 5

from itertools import count, izip

def enumerate(L, n=0):
    return izip( count(n), L)

# if 2.5 has no count
def count(n=0):
    while True:
        yield n
        n+=1

现在h = list(enumerate(xrange(2000, 2005), 1))可以使用了。

from itertools import count, izip

def enumerate(L, n=0):
    return izip( count(n), L)

# if 2.5 has no count
def count(n=0):
    while True:
        yield n
        n+=1

Now h = list(enumerate(xrange(2000, 2005), 1)) works.


回答 6

枚举是微不足道的,因此重新实现它以接受一个开始:

def enumerate(iterable, start = 0):
    n = start
    for i in iterable:
        yield n, i
        n += 1

请注意,这没有使用没有开始参数的枚举不会破坏代码。另外,此oneliner可能更优雅,甚至可能更快,但破坏了枚举的其他用途:

enumerate = ((index+1, item) for index, item)

后者纯粹是胡说八道。@邓肯正确的包装。

enumerate is trivial, and so is re-implementing it to accept a start:

def enumerate(iterable, start = 0):
    n = start
    for i in iterable:
        yield n, i
        n += 1

Note that this doesn’t break code using enumerate without start argument. Alternatively, this oneliner may be more elegant and possibly faster, but breaks other uses of enumerate:

enumerate = ((index+1, item) for index, item)

The latter was pure nonsense. @Duncan got the wrapper right.


回答 7

>>> list(enumerate(range(1999, 2005)))[1:]
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]
>>> list(enumerate(range(1999, 2005)))[1:]
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

回答 8

h = [(i + 1, x) for i, x in enumerate(xrange(2000, 2005))]

h = [(i + 1, x) for i, x in enumerate(xrange(2000, 2005))]


回答 9

好的,我在这里有点愚蠢……为什么不只做类似的事情
[(a+1,b) for (a,b) in enumerate(r)]呢?如果您无法运行,则也没有问题:

>>> r = range(2000, 2005)
>>> [(a+1,b) for (a,b) in enumerate(r)]
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

>>> enumerate1 = lambda r:((a+1,b) for (a,b) in enumerate(r)) 

>>> list(enumerate1(range(2000,2005)))   # note - generator just like original enumerate()
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

Ok, I feel a bit stupid here… what’s the reason not to just do it with something like
[(a+1,b) for (a,b) in enumerate(r)] ? If you won’t function, no problem either:

>>> r = range(2000, 2005)
>>> [(a+1,b) for (a,b) in enumerate(r)]
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

>>> enumerate1 = lambda r:((a+1,b) for (a,b) in enumerate(r)) 

>>> list(enumerate1(range(2000,2005)))   # note - generator just like original enumerate()
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

回答 10

>>> h = enumerate(range(2000, 2005))
>>> [(tup[0]+1, tup[1]) for tup in h]
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

由于这有点冗长,因此建议您编写自己的函数以对其进行概括:

def enumerate_at(xs, start):
    return ((tup[0]+start, tup[1]) for tup in enumerate(xs))
>>> h = enumerate(range(2000, 2005))
>>> [(tup[0]+1, tup[1]) for tup in h]
[(1, 2000), (2, 2001), (3, 2002), (4, 2003), (5, 2004)]

Since this is somewhat verbose, I’d recommend writing your own function to generalize it:

def enumerate_at(xs, start):
    return ((tup[0]+start, tup[1]) for tup in enumerate(xs))

回答 11

我不知道这些帖子如何变得比以下内容更复杂:

# Just pass the start argument to enumerate ...
for i,word in enumerate(allWords, 1):
    word2idx[word]=i
    idx2word[i]=word

I don’t know how these posts could possibly be made more complicated then the following:

# Just pass the start argument to enumerate ...
for i,word in enumerate(allWords, 1):
    word2idx[word]=i
    idx2word[i]=word

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