Regex for non decimal integer considering exponents - regex

Question

I am looking for a Regex for non decimal integer considering exponents and honestly I have tried a lot before asking here.
The regex should
match 1.23E4,1.2334576E34, 122E3,123,456 etc.
not match 1.234E2 (since it expands to 123.4).
should not match 1.22 and so on.
My try was
^[+-]?([0-9]*\\.?[0-9]+|[0-9]+\\.?[0-9]*)([eE][+]?[0-9]+)?$
However as you can see I am not calculating the exponent so that after expansion I should be able to tell that a value X after expanding does not contain a decimal.
Is there any way to extract the number of digits after the decimal . and compare it with exponent so that I can be sure that after expanding it will not contain a decimal.
For the info only a regex that can work in runtime will work for me.
Please help me guys...

Answer 1

ok, so this is only if you really need this for some weird regexp-only validation. it's written in python 3 and it makes no attempt to be compact (there's no limitation except available memory in the size of a regexp in python).
def over(n):
'''make aregexp for an exponent of n or more'''
assert n < 100
return r'([1-9]\d{2,}|%s)' % '|'.join(str(i) for i in range(n, 100))
def make_decimal(n_digits, n_decimal):
'''make a regexp for a number with an "E" with the given number of significant digits and decimal places'''
assert n_decimal < n_digits
assert 100 > n_decimal >= 0
if n_decimal:
return r'\d{%d}.\d{%d}E%s' % (n_digits-n_decimal, n_decimal, over(n_decimal))
else:
return r'\d{%d}E\d+'
def make_e(n_digits):
'''make a regexp for an integer with an "E" with the given number of significant digits'''
return '|'.join(make_decimal(n_digits, i) for i in range(n_digits))
def make_regexp(max_digits):
'''make a regexp for a decimal integer with up to the given number of significant digits'''
assert max_digits < 100
return r'(\d+|%s)' % '|'.join(make_e(i) for i in range(max_digits+1))
here's some test code.
from re import compile
rx = make_regexp(8)
m = compile('^%s$' % rx)
for n in ['1.23E4', '1.2334576E34', '122E3', '123', '456']:
assert m.match(n), n
for n in ['1.234E2', '1.22']:
assert not m.match(n), n
for up to significant 8 digits (to the left of E), which seems a reasonable limit, the regexp generated is 8774 digits long. you could reduce this significantly (for example, see https://stackoverflow.com/a/17840228/181772), but what's the need (the regular expression engine is capable of generating a much smaller internal automaton from this)?

Answer 2

Description
It's not impossible, but rather difficult and the expression will really start to get out of hand. Take this 2831 character monster which:
validates a number with exponent will expand to an integer
requires a number to be in 123.456e7890 or 1234.678e1,234,567
if the exponent contains commas they must appear in the correct comma delimited three digit groupings
supports only numbers upto 99 places after the decimal point
As written here it does require the use of the x option which will ignore white space and comments. The expression could be shortened to about 2041 by replacing the [eE] with e and using the i option; and [0-9] with \d however this will slightly reduce performance because \d class contains all unicode characters and not just 0-9.
^
(?=.*?[eE][0-9]{1,3}(?:,[0-9]{3})*|[0-9]*$) # validate commas are in the correct order
(?=[0-9]+\. # match the integer portion of a real number
(?=
[0-9]{1,99}[eE][1-9](?:,?[0-9]){2,}
|[0-9]{1,9}[eE][1-9],?[0-9]
|[0-9]{10,19}[eE][2-9],?[0-9]
|[0-9]{20,29}[eE][3-9],?[0-9]
|[0-9]{30,39}[eE][4-9],?[0-9]
|[0-9]{40,49}[eE][5-9],?[0-9]
|[0-9]{50,59}[eE][6-9],?[0-9]
|[0-9]{60,69}[eE][7-9],?[0-9]
|[0-9]{70,79}[eE][89],?[0-9]
|[0-9]{80,89}[eE][9],?[0-9]
|[0-9]{90,99}[eE][1-9],?[0-9]
|(?=[0-9]{90}(?=.*?[eE]9)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{80}(?=.*?[eE]8)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{70}(?=.*?[eE]7)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{60}(?=.*?[eE]6)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{50}(?=.*?[eE]5)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{40}(?=.*?[eE]4)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{30}(?=.*?[eE]3)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{20}(?=.*?[eE]2)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?=[0-9]{10}(?=.*?[eE]1)(?:[eE].,?[0-9]|[0-9]{1}[eE].,?[1-9]|[0-9]{2}[eE].,?[2-9]|[0-9]{3}[eE].,?[3-9]|[0-9]{4}[eE].,?[4-9]|[0-9]{5}[eE].,?[5-9]|[0-9]{6}[eE].,?[6-9]|[0-9]{7}[eE].,?[7-9]|[0-9]{8}[eE].,?[89]|[0-9]{9}[eE].,?9))
|(?:[eE][0-9]|[0-9]{1}[eE][1-9]|[0-9]{2}[eE][2-9]|[0-9]{3}[eE][3-9]|[0-9]{4}[eE][4-9]|[0-9]{5}[eE][5-9]|[0-9]{6}[eE][6-9]|[0-9]{7}[eE][7-9]|[0-9]{8}[eE][89]|[0-9]{9}[eE]9)
)
|(?=[0-9]+[eE]) # integers
)
[+-]?
([0-9]*\.?[0-9]+|[0-9]+\.?[0-9]*)
[eE][+]?((?:,?[0-9]+)+)
As written here the expression uses the x option which ignores white space
Example
Sample Text
1.2334576E34
1.23E4
1.2334576E34
122E3,123,456
1.234
1.234E2
Matches
[0] => 1.2334576E34
[1] => 1.23E4
[2] => 1.2334576E34
[3] => 122E3,123,456