from pyparsing import delimitedList, Word, alphas, Combine

str1 = Combine(Word(alphas) + "+" + Word(alphas))     # "x+y"
str2 = Combine(Word(alphas) + "++")                   # "c++"
str3 = Word(alphas)                                   # "z"

strs = str1 | str2 | str3

f = delimitedList(strs, "+")
print(f.parseString("x+y+c+++z+x+z+++x"))