I have several thousand lines like:
"The sequence 1,-2,-1,2,1,-2,-1,2,... with g.f. (1-2x)/(1+x^2) has a(n) = cos(Pi*n/2)-2*sin(Pi*n/2). - Paul Barry, Oct 18 2004"
and I need to find the position, if any, of the date that show up as abbreviations like 'Aug 03'. For this reason I wrote a function _find_all_positions that takes as input a string and a date specifier from 'Jan 01' to 'Dec 31' in a for loop.
def _add_zero(value: int) -> str:
"""add zero to number with digits < 2"""
value_str = str(value)
digits = len(value_str)
if digits < 2:
value_str = '0' + value_str
return value_str
def get_date() -> list:
"""Get dates for author(s) search, from ' Jan 01' to ' Dec 31' """
dates = list()
months = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
for month in months:
for day in range(1, 32):
dates.append(' ' + month + ' ' + ParserUtilities._add_zero(day))
return dates
def _find_all_positions(string: str, sub: str):
"""Find all occurrences of a substring in a string"""
start = 0
while True:
start = string.find(sub, start)
if start == -1:
return
yield start
start += len(sub) # use start += 1 to find overlapping matches
The task is quite slow and I would like to know if with Regular Expression it would be possible to speed up the search
You can put all months in one regular expression:
def find_all_positions(text):
for match in re.finditer('(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) ([012][0-9]|30|31)', text):
yield math.start()