parse own chem formula

chem_parser.py

+# from http://www.dalkescientific.com/writings/NBN/parsing_with_ply.html
+
+
+# A grammar for chemical equations like "H2O", "CH3COOH" and "H2SO4"
+# Uses David Beazley's PLY parser.
+# Implements two functions: count the total number of atoms in the equation and
+#   count the number of times each element occurs in the equation.
+
+import ply.lex as lex
+import ply.yacc as yacc
+
+tokens = (
+    "SYMBOL",
+    "NUM",
+    "DOT",
+    'LPAREN',
+    'RPAREN'
+)
+
+t_SYMBOL = (
+    r"C[laroudsemf]?|Os?|N[eaibdpos]?|S[icernbmg]?|P[drmtboau]?|"
+    r"H[eofgas]?|A[lrsgutcm]|B[eraik]?|Dy|E[urs]|F[erm]?|G[aed]|"
+    r"I[nr]?|Kr?|L[iaur]|M[gnodt]|R[buhenaf]|T[icebmalh]|"
+    r"U|V|W|Xe|Yb?|Z[nr]|D")
+t_DOT  = r'\.'
+t_LPAREN  = r'\['
+t_RPAREN  = r'\]'
+
+def t_NUM(t):
+    r"\d+"
+    t.value = int(t.value)
+    return t
+
+t_ignore  = ' \t'
+
+def t_error(t):
+    raise TypeError("Unknown text '%s'" % (t.value,))
+
+
+lexer1 = lex.lex()
+
+def p_chemical_equation(p):
+    """
+    chemical_equation :
+    chemical_equation : species_list
+    """
+    if len(p) == 1:
+        # the empty string means there are no atomic symbols
+        p[0] = {}
+    else:
+        p[0] = p[1]
+
+def p_species_list(p):
+    "species_list :  species_list species"
+    p[1].update(p[2])
+    p[0] = p[1]
+
+def p_species(p):
+    "species_list : species"
+    p[0] = p[1]
+
+def p_single_species(p):
+    """
+    species : SYMBOL
+    species : SYMBOL NUM
+    species : SYMBOL LPAREN NUM RPAREN
+    species : SYMBOL LPAREN NUM DOT DOT NUM RPAREN
+    """
+    if len(p) == 2:
+        p[0] = {p[1]: (1,1)}
+    elif len(p) == 3:
+        p[0] = {p[1]: (p[2],p[2])}
+    elif len(p) == 5:
+        p[0] = {p[1]: (p[3],p[3])}
+    elif len(p) == 8:
+        p[0] = {p[1]: (p[3],p[6])}
+
+def p_error(p):
+    raise TypeError("unknown text at %r" % (p.value,))
+
+parser1 = yacc.yacc()#(debug=0, optimize=0)
+
+def txt2dict(txt):
+    return parser1.parse(txt, lexer=lexer1)
\ No newline at end of file