char=str('DOTR')

a=range(0,18)

mylist=['DOTR00','DOTR01',...,'DOTR17']

>>> string = "DOTR"
>>> for i in range(0, 18):
...     print("DOTR{}".format(str(i).zfill(2)))
...
DOTR00
DOTR01
DOTR02
DOTR03
DOTR04
DOTR05
DOTR06
DOTR07
DOTR08
DOTR09
DOTR10
DOTR11
DOTR12
DOTR13
DOTR14
DOTR15
DOTR16
DOTR17
>>>

>>> my_list = ["DOTR{}".format(str(i).zfill(2)) for i in range(18)]
>>> my_list
['DOTR00', 'DOTR01', 'DOTR02', 'DOTR03', 'DOTR04', 'DOTR05', 'DOTR06', 'DOTR07', 'DOTR08', 'DOTR09', 'DOTR10', 'DOTR11', 'DOTR12', 'DOTR13', 'DOTR14', 'DOTR15', 'DOTR16', 'DOTR17']
>>>

>>> mylist = [char+'{0:02}'.format(i) for i in a]
>>> mylist
['DOTR00', 'DOTR01', 'DOTR02', 'DOTR03', 'DOTR04', 'DOTR05', 'DOTR06', 'DOTR07', 'DOTR08', 'DOTR09', 'DOTR10', 'DOTR11', 'DOTR12', 'DOTR13', 'DOTR14', 'DOTR15', 'DOTR16', 'DOTR17']

char = str('DOTR')
a=range(0,18)
b = []
for i in a:
    b.append(char + str(i))
print(b)

mylist = ['DOTR%02d'%i for i in range(18)]

mylist = ['%s%02d'%(char,i) for i in a]

mylist = ['{}{:02d}'.format(char,i) for i in a]

[<expr> for <var> in <iterable>]