Question

I am trying to scan some documents to find dates for a classification problem. After reading around here and some other places I have constructed the following regular expression

months='['+'|'.join(calendar.month_abbr[1:])+'|'+'|'.join(calendar.month_name[1:])+']'
techPart='+\\.*\\s*\\d{1,2}[,]?[\\s*][1|2]\\d{3}'
dateExpr=months+techPart

I am testing it on this string

newString='Mar. 31, 2011 Dec. 31, 2010 bananas Mar. 31, 2011 too much malarky September 1, 1992 redundant Dec. 31, 2010  September 29, 1999  March 12 2004 ddfd  March.    13 2019 ddfd  Mac.    13 2019 ddfd'

and when I run it like this

for date in re.findall(dateExpr,newString):
print date

I get this

Mar. 31, 2011
Dec. 31, 2010
Mar. 31, 2011
September 1, 1992
Dec. 31, 2010
September 29, 1999
March 12 2004
March.    13 2019
Mac.    13 2019    #here is my problem

Answer 1

In your months regex, you are using square brackets, giving something like [Jan|Feb|Mar|...]. That is wrong. Square brackets are for character classes and match one of any character in the brackets, so this will match J or a or n or | or F, etc. Instead you want to use parentheses:

months='(?:'+'|'.join(calendar.month_abbr[1:])+'|'+'|'.join(calendar.month_name[1:])+')'

You need the ?: because findall returns only captured groups, so we need to mark this group as noncapturing.

You have the same problem later in your regex where you do [1|2]. You want (?:1|2), or just [12].