I would like to create a dictionary to split all elements of a molecular formula. I tried using re module
Formula="C16H21NO2Na3"
pat = re.compile('(?P<name>[A-Z][a-z]+)\[0-9]+(?P<name2>[0-9]+)')
molecule= pat.findall(Formula)
print (molecule)
I expected this return:
{'C': 16, 'H': 21, 'N': '', 'O': 2, 'Na': 3}
you were pretty close
pat = re.compile('(?P<name>[A-Z][a-z]?)(?P<value>[0-9]*)')
name is an uppercase letter followed by zero or 1 lowercase letters and value is 0 or more digits
then to make it a dict you just call dict on it
matches = pat.findall(Formula)
data = dict(matches)
# {'C': '16', 'H': '21', 'N': '', 'O': '2', 'Na': '3'}
you could be more sophisticated with the dict as follows
data = {k: int(v) if v else 1 for k,v in matches}
# {'C': 16, 'H': 21, 'N': 1, 'O': 2, 'Na': 3}
# the following will also work, which is slightly shorter (thanks @copperfield)
data = {k: int(v or 1) for k,v in matches}
# {'C': 16, 'H': 21, 'N': 1, 'O': 2, 'Na': 3}