Fastest way to insert these dashes in python string?

Question

So I know Python strings are immutable, but I have a string:

c['date'] = "20110104"

Which I would like to convert to

c['date'] = "2011-01-04"

My code:

c['date'] = c['date'][0:4] + "-" + c['date'][4:6] + "-" + c['date'][6:]

Seems a bit convoluted, no? Would it be best to save it as a separate variable and then do the same? Or would there basically be no difference?

score 25 · Accepted Answer · answered Jan 17 '13 at 20:59

25

You could use .join() to clean it up a little bit:

d = c['date']
'-'.join([d[:4], d[4:6], d[6:]])

answered Jan 17 '13 at 20:59

Blender

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If performance is what OP means by "faster", I've found that `'-'.join((d[:4],d[4:6],d[6:]))` is marginally faster (i.e. tuple instead of a list). – mgilson Jan 17 '13 at 21:00
1

This looks very clean and pythonic to me :) – LittleBobbyTables Jan 17 '13 at 21:02
Simple and elegant solution! – Abhishek Upadhyaya Aug 20 '20 at 20:24

Colonel Panic · Answer 2 · 2020-07-22T21:39:50.337

10

Dates are first class objects in Python, with a rich interface for manipulating them. The library is datetime.

> import datetime
> datetime.datetime.strptime('20110503','%Y%m%d').date().isoformat()
'2011-05-03'

Don't reinvent the wheel!

edited Jul 22 '20 at 21:39

answered Jan 17 '13 at 22:51

Colonel Panic

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thus: `c['date'] = pd.to_datetime(c['date'], format = '%Y%m%d')` . See: https://stackoverflow.com/questions/26763344/convert-pandas-column-to-datetime – Richard Oct 03 '20 at 02:57

score 6 · Answer 3 · answered Jan 17 '13 at 20:59

6

You are better off using string formatting than string concatenation

c['date'] = '{}-{}-{}'.format(c['date'][0:4], c['date'][4:6], c['date'][6:])

String concatenation is generally slower because as you said above strings are immutable.

answered Jan 17 '13 at 20:59

GWW

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Rob Cowie · Answer 4 · 2013-01-17T21:11:09.950

s = '20110104'


def option_1():
    return '-'.join([s[:4], s[4:6], s[6:]])

def option_1a():
    return '-'.join((s[:4], s[4:6], s[6:]))

def option_2():
    return '{}-{}-{}'.format(s[:4], s[4:6], s[6:])

def option_3():
    return '%s-%s-%s' % (s[:4], s[4:6], s[6:])

def option_original():
    return s[:4] + "-" + s[4:6] + "-" + s[6:]

Running %timeit on each yields these results

option_1: 35.9 ns per loop
option_1a: 35.8 ns per loop
option_2: 36 ns per loop
option_3: 35.8 ns per loop
option_original: 36 ns per loop

So... pick the most readable because the performance improvements are marginal

score 1 · Answer 5 · answered Jan 17 '13 at 20:59

1

I'd probably do so this way, not that there's a great deal of gain:

d = c['date']
c['date'] = '%s-%s-%s' % (d[:4], d[4:6], d[6:])

The big improvement (imho) is avoiding string concatenation.

answered Jan 17 '13 at 20:59

g.d.d.c

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score 1 · Answer 6 · answered Jan 17 '13 at 22:03

1

I'm not usually the guy saying "use regex," but this is a good use-case for it:

import re    
c['date']=re.sub(r'.*(\w{4})(\w{2})(\w{2}).*',r"\1-\2-\3",c['date'])

answered Jan 17 '13 at 22:03

SuperFamousGuy

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score 1 · Answer 7 · edited Feb 11 '15 at 08:44

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I am not sure if you want to convert it to a proper datetime object or rather just hard code the format, you can do the following:

from datetime import datetime
result = datetime.strptime(c['date'], '%Y%m%d')
print result.date().isoformat()

Input: '20110104'

Output: '2011-01-04'

edited Feb 11 '15 at 08:44

Community

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answered Jan 17 '13 at 23:09

user1613017

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score 1 · Answer 8 · answered May 14 '20 at 12:37

1

Add hyphen to a series of strings to datetime

import datetime
for i in range (0,len(c.date)):
  c.date[i] = datetime.datetime.strptime(c.date[i],'%Y%m%d').date().isoformat()

answered May 14 '20 at 12:37

Rohan Sarin

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Fastest way to insert these dashes in python string?

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