I'm trying to match numbers in scientific notation (regex from here):
scinot = re.compile('[+\-]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+)')
re.findall(scinot, 'x = 1e4')
['1e4']
re.findall(scinot, 'x = c1e4')
['1e4']
I'd like it to match x = 1e4 but not x = c1e4. What should I change?
Update: The answer here has the same problem: it incorrectly matches 'x = c1e4'.
Add anchor at the end of regex and alternative space or equal sign before the number:
[\s=]+([+-]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+))$
x = 1e6.
x = 1e4 or 1e4 alone?1e6 from x = 1e6. Sorry about the confusion. re.findall('^[+-]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+)$', 'x = 1e6') returns [].[\s=], see my edit.= is not part of the match; right now I get ['=1e6'] for x=1e6.Simply add [^\w]? to exclude all alphanumeric characters that precede your first digit:
[+\-]?[^\w]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+)
Technically, the \w will also exlude numeric characters, but that's fine because the rest of your regex will catch it.
If you want to be truly rigorous, you can replace \w with A-Za-z:
[+\-]?[^A-Za-z]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+)
Another sneaky way is to simply add a space at the beginning of your regex - that will force all your matches to have to begin with whitespace.
c1e4 unfortunately. Also, if I add a space (nice idea!), I won't be able to match x=1e4 anymore.scinot = re.compile('[-+]?[\d]+\.?[\d]*[Ee](?:[-+]?[\d]+)?')
This regex would help you to find all the scientific notation in the text.
By the way, here is the link to the similar question: Extract scientific number from string
re.findall('([-+])?(\d+)(\.\d*)?[eE]([-+]?\d+)*', 'x = c1e6') returns [('', '1', '', '6')]
re.findall('[-+]?[0-9]+\.?[0-9]*[Ee](?:\ *[-+]?\ *[0-9]+)?', 'x = c1e6') incorrectly matches ['1e6']