Identify integer, string and floating point literals

Question

I am new to Python and I am stuck with a problem. I have an input file which contains data as below:

12345    67890     afghe
abcde    23456     0abcd
34567    __fred01  45678
123.456  12345a    123.
.456     ab00cd    00ab00

By using regular expression is need to parse each literal and classify whether the literal is a string or an integer or a floating point. The code snippet is somewhat like below:

def processtoken(token):
    #Replace the following line with your code to classify
    # the string in 'token' according to your three Regular
    # Expressions and print the appropriate message.
    print('Inside Process Token')

    match = re.search(r'(0|[1-9][0-9]*|0[oO]?[0-7]+|0[xX][0-9a-fA-F]+|0[bB][01]+)[lL]?', token)
    matchfp = re.search(r'^[0-9]+\.?[0-9]+$',token)
    if match:
        print(match.group(),'matches INT')
    elif matchfp:
        print(matchfp.group(),'matches FP')

My issue is how can I structure the code to validate multiple regex conditions for each token passed. As of now the floating point if the condition is not validated. I want to check the token for, first integer regex if it matches or if it matches floating point regex or it matches string. Any help will be appreciated.

Answer 1

I would structure the problem as follows:

integer_regex = r"^...$"
float_regex = r"^...$"
string_regex = r"^...$"

def processToken(token):

    if re.search(integer_regex, token):
        print(token, 'matches INT')
    elif re.search(float_regex, token):
        print(token, 'matches FLOAT')
    elif re.search(string_regex, token):
        print(token, 'matches STR')
    else:
        print(token, 'unknown')

Filling your patterns into the *_regex variables above.

Also note, your float pattern is no good, as it also matches int:

r'^[0-9]+\.?[0-9]+$'

Since the decimal point is optional. You might be better off breaking the pattern into an alternation with three options, starts with '.', ends with '.' or contains a '.' between numbers. Also, in your integer pattern, the '?' in the octal section is incorrect:

0[oO]?[0-7]+

at this point we're trying to commit to octal so the prefix is not optional:

0[oO][0-7]+

You got this correct for hex and binary.