how can I generate a string (or Pandas series) like below:
a1,a2,a3,a4,...,a19
the following works, but I would like to know a shorter way
my_str = ""
for i in range(1, 20):
comma = ',' if i!= 19 else ''
my_str += "d" + str(i) + comma
Add a comment
|
3 Answers
You can just use a list comprehension to generate the individual elements (using string concatenation or str.format), and then join the resulting list on the separator string (the comma):
>>> ['a{}'.format(i) for i in range(1, 20)]
['a1', 'a2', 'a3', 'a4', 'a5', 'a6', 'a7', 'a8', 'a9', 'a10', 'a11', 'a12', 'a13', 'a14', 'a15', 'a16', 'a17', 'a18', 'a19']
>>> ','.join(['a{}'.format(i) for i in range(1, 20)])
'a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19'
Comments
What about:
s = ','.join(["a%d" % i for i in range(1,20)])
print(s)
Output:
a1,a2,a3,a4,a5,a6,a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19
(This uses a generator expression, which is more efficient than joining over a list comprehension -- only slightly, with such a short list, however) This now uses a list comprehension! See comments for an interesting read about why list comprehensions are more appropriate than generator expressions for join.
6 Comments
Dan D.
You have redundant parenthesis:
','.join("a%d" % i for i in range(1,20))
poke
Unlike common belief, joining on a generator expression is not more efficient than joining on a list directly. See this answer for details.
jedwards
@DanD. they're not redundant, they're explicit -- if you were to need additional arguments to the outer function (
join, in this case), you would need them.jedwards
@poke, I could never argue with Raymond Hettinger -- will update accordingly.
jedwards
@poke, I agree. But in the spirit of "explicit is better than implicit", I tend to leave them, to avoid future confusion. If the same generator were applied to say,
max(..., key=...), it would be an odd use indeed, but you would need the parens. |
Adding onto what poke said (which I found to be the most helpful), but bringing it into 2022:
[f'a{i}' for i in range(1, 21)]
