How to filter out this list, so that we are left with only a list of strings that are in yyyy-mm-dd format?
2021-11-11
2021-10-01
some_folder
some_other_folder
so that we end up with a list like so:
2021-11-11
2021-10-01
Also what if the list has a prefix?
root/2021-11-11
root/2021-10-01
user/some_folder
root/some_other_folder
and we wanted to end up with:
root/2021-11-11
root/2021-10-01
I would let datetime module handle that for me using strptime. If it is not in '%Y-%m-%d' format, it raises ValueError :
import datetime
lst = ['2021-11-11', '2021-10-01', 'some_folder', 'some_other_folder',
'root/2021-11-11', 'root/2021-10-01',
'user/some_folder', 'root/some_other_folder']
def filter_(s):
last_part = s.rsplit('/', maxsplit=1)[-1]
try:
datetime.datetime.strptime(last_part, '%Y-%m-%d')
return True
except ValueError:
return False
print([i for i in lst if filter_(i)])
output :
['2021-11-11', '2021-10-01', 'root/2021-11-11', 'root/2021-10-01']
rsplit the lines using slash and maxsplit=1 then take the second.[-2] if the strings all have a / at the end?You can use the re library for this. Something like this.
Edit: Changed my answer because of @SorousHBakhtiary's comment about an exception I forgot that happens when you modify an iterable object while iterating it.
import re
li = [
'root/2021-11-11',
'root/2021-10-01',
'user/some_folder',
'root/some_other_folder',
]
new_list = li.copy()
for string in new_list:
if not re.fullmatch('.*\d{4}-\d{2}-\d{2}$',string):
li.remove(string)
This can also be done in one line using list comprehension:
li = [
'root/2021-11-11',
'root/2021-10-01',
'user/some_folder',
'root/some_other_folder',
]
li = [string for string in li if re.fullmatch('.*\d{4}-\d{2}-\d{2}$',string)]
২০২২-০৫-১৯.for string in list.copy().
re.fullmatch() call to look like re.fullmatch('.*\d{4}-\d{2}-\d{2}$',string)``. The .*` at the start and the $ at the end of the regular expression will make the program look for any string that ends with something in the yyyy-mm-dd format.>>> import re
>>>
>>> filter_pattern = re.compile(r'.*\d{4}-\d{2}-\d{2}$')
>>>
>>> lst = [
... '2021-11-11', '2021-10-01', 'some_folder',
... 'some_other_folder', 'root/2021-11-11', 'root/2021-10-01',
... 'user/some_folder', 'root/some_other_folder'
... ]
>>>
>>> lst = [i for i in lst if (len(filter_pattern.findall(i) > 0)]
>>>
>>> lst
