EZmachining

String Expression Calculation

The project can translate infix expressions to postfix(str to tuple with members of different types). And can calculate if needed.

Used algorithm from Алгоритм сортировочной станции , also known as Shunting yard algorithm. I used less detailed russian wiki and had no choice but improove it a little - degree('^') handler added. Unary minus was created too - better fix negatives in postfixing than in calculating.

You can see project here https://github.com/wolkolak/postfixcalc

Initially I tried to find suitable module on PYPI but failed unfortunately:

Firstly expression can contain functions: sin, pow, mod, neg, etc. Most projects can't work with that.

Secondly module should handle logic operators too: '<' , '==' , 'AND' , 'OR' , etc. And variables, too.

The third point - i need to create postfix expressions tens of times, and calculate it thousands of times. Because of that postfix expressions had to be turned into tuples. Entire module is a part of my CNC interpreter.

Fourth point - I don't want to see "divided by zero error", so calculator should return None in that case.

To calculate infix expression You need next functions:

1. tokenize
   a = tokenize('-2^ -(sin(5)3)')
   print(a)
   ->>['-', 2.0, '^', '(', '-', '(', 'sin', '(', 5.0, ')', '', 3.0, ')', ')']'

2. tokensPostfixing
   b = tokensPostfixing(a)
   print(b)
   -->(2.0, 5.0, 'sin', 3.0, '*', '', '^', '')'

3. postfixTokenCalc
   print(postfixTokenCalc(b, DICT_VARS=None))
   -0.8342390624578879
   dict_A = {'x': 5}
   print(postfixTokenCalc(('x', 1.0, '+', 6, '=='), DICT_VARS=dict_A))
   True

   print('complex?: ', postfixTokenCalc((5, 3j, '-',)))
   complex?: (5-3j)

As you can see, even complex numeric type didn't break the program. For now. I do not require complex in CNC, so I run only one test with it.
And '=' is not a mathematical or logical operator - your expression for calculation should not contain assignments in the middle(You can start from "=" though). Best time to handle assignments would be after tokenization, I believe.

If You need different operators and functions (or sin in radians for example), look at the followed dicts and modify:

• OPERATORs_DICT_math:                     +, -, /, *, ^
• OPERATORs_DICT_logic_L                    AND, NOT, OR', GT...
• OPERATORs_DICT_func_1                   sqrt, pow1', abc, neg, mod, sin ...       # functions with 1 arg
• OPERATORs_DICT_func_2                   pow2                                                   # functions with 2 args
• OPERATORs_DICT_compare1               <, =, > (= should only be used as a part of '<=', '>=', '==' as explained above)
• OPERATORs_DICT_compare2               <=, ==, <>, >=
• OPERATORs_PRECEDENCE_DICT       functions and operators precedence, obviously

Also, You can use DICT_VARS to look for your variables. You can throw away some operators like 'GT' or 'EQ' - this is the same as '>' and '==' in some CNC and other languages, and not required for You, probably.

PS: This is my first attempt to share code with others, tell me if something wrong.