Why does my regex numbers match a string like $ab? I want it to only match sequences of decimal digits, 0-9 either followed by a ${ or a $ and followed by a } in the first case and nothing in the second case.
import re
numbers = re.compile('\$\{[0-9]*\}|\$[0-9]*') # ${ANY_SEQUENCE_OF_DIGITS} or $ANY_SEQUENCE_OF_DIGITS
if numbers.match("$ab"):
print 'matches'
This sample code prints 'matches'
Keep in mind that * means zero or more. It matches because youf have a $ and zero digits after it. match() does not require the entire string to be matched, just the beginning.
If you want to match non-empty digits and nothing extra after it:
numbers = re.compile(r'\$\{[0-9]+\}$|\$[0-9]+$')
This uses + to require "1 or more" digits, as well as explicit $ to indicate that there can't be extra stuff at the end (you can leave those off if you do want to allow extra characters on the end)
You're matching $ because you have [0-9]*
What you probably want is this
re.compile('\$\{[0-9]+\}|\$[0-9]+')
If you just had:
import re
numbers = re.compile('\$\{[0-9]*\}') # ${ANY_SEQUENCE_OF_DIGITS} or $ANY_SEQUENCE_OF_DIGITS
if numbers.match("$ab"):
print 'matches'
Then it would not print "matches"
However, since you added |\$[0-9]* you are essentially saying "or match $ followed by zero or more digits." $ab indeed satisfies "$ followed by zero or more digits" and so a match is found.
