This recipe will insert multiplication symbols and convert all grouping symbols to equivalent parentheses. Uses the tokenize module for compact coding.
Python, 57 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | def toProperFormula(s):
"""
Given formula string, returns a modified formula with missing
multiplication symbols and grouping symbols [],{} replaced by parentheses.
Only primitive error checking for mismatched grouping symbols is shown in
this recipe.
author: ernesto.adorio@gmail.com, ernie@extremecomputing.org
"""
import tokenize
from cStringIO import StringIO
f = StringIO(s)
# Make variables mutable to child function.
formula = [""]
prevtoken = [""]
prevsymbol = [""]
closers = []
def handle_token(type, token, (srow, scol), (erow, ecol), line):
token = str(token)
symbol = tokenize.tok_name[type]
if symbol == "OP":
if token == ")":
if closers.pop() != "(": raise FormulaError('Error: "' +line[:ecol] + '" unbalanced ).')
elif token == "]":
if closers.pop() != "[": raise FormulaError('Error: "' +line[:ecol] + '" unbalanced ].')
token = ")"
elif token == "}":
if closers.pop() != "{": raise FormulaError('Error: "' +line[:ecol] + '" unbalanced }.')
token = ")"
elif token in ["(", "[", "{"]:
closers.append(token)
if prevtoken[0] == ")" or prevsymbol[0] == "NUMBER":
formula[0] += "*"
token = "("
elif symbol in ["NAME", "NUMBER"]:
if prevtoken[0] == ")" or prevsymbol[0] in ["NAME", "NUMBER"]:
formula[0] += "*"
formula[0] += token
prevtoken[0] = token
prevsymbol[0] = symbol
tokenize.tokenize(f.readline, handle_token)
return formula[0]
print toProperFormula("2 ( 23.45x - 4y) [34 - 5 x] + w^[atan2(2y, 4x)] 5")
"""
2*(23.45*x-4*y)*(34-5*x)+w^(atan2(2*y,4*x))*5
"""
|
This formula allows an ordinary user to input a formula string more naturally for processing by a program.
