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# SimpleCalc.py
#
# Demonstration of the parsing module,
# Sample usage
#
# $ python SimpleCalc.py
# Type in the string to be parse or 'quit' to exit the program
# > g=67.89 + 7/5
# 69.29
# > g
# 69.29
# > h=(6*g+8.8)-g
# 355.25
# > h + 1
# 356.25
# > 87.89 + 7/5
# 89.29
# > ans+10
# 99.29
# > quit
# Good bye!
#
#
# Uncomment the line below for readline support on interactive terminal
# import readline
from pyparsing import ParseException, Word, alphas, alphanums
import math
# Debugging flag can be set to either "debug_flag=True" or "debug_flag=False"
debug_flag=False
variables = {}
from fourFn import BNF, exprStack, fn, opn
def evaluateStack( s ):
op = s.pop()
if op == 'unary -':
return -evaluateStack( s )
if op in "+-*/^":
op2 = evaluateStack( s )
op1 = evaluateStack( s )
return opn[op]( op1, op2 )
elif op == "PI":
return math.pi # 3.1415926535
elif op == "E":
return math.e # 2.718281828
elif op in fn:
return fn[op]( evaluateStack( s ) )
elif op[0].isalpha():
if op in variables:
return variables[op]
raise Exception("invalid identifier '%s'" % op)
else:
return float( op )
arithExpr = BNF()
ident = Word(alphas, alphanums).setName("identifier")
assignment = ident("varname") + '=' + arithExpr
pattern = assignment | arithExpr
if __name__ == '__main__':
# input_string
input_string=''
# Display instructions on how to quit the program
print("Type in the string to be parsed or 'quit' to exit the program")
input_string = input("> ")
while input_string != 'quit':
if input_string.lower() == 'debug':
debug_flag=True
input_string = input("> ")
continue
# Reset to an empty exprStack
del exprStack[:]
if input_string != '':
# try parsing the input string
try:
L=pattern.parseString( input_string, parseAll=True )
except ParseException as err:
L=['Parse Failure',input_string]
# show result of parsing the input string
if debug_flag: print(input_string, "->", L)
if len(L)==0 or L[0] != 'Parse Failure':
if debug_flag: print("exprStack=", exprStack)
# calculate result , store a copy in ans , display the result to user
try:
result=evaluateStack(exprStack)
except Exception as e:
print(str(e))
else:
variables['ans']=result
print(result)
# Assign result to a variable if required
if L.varname:
variables[L.varname] = result
if debug_flag: print("variables=",variables)
else:
print('Parse Failure')
print(err.line)
print(" "*(err.column-1) + "^")
print(err)
# obtain new input string
input_string = input("> ")
# if user type 'quit' then say goodbye
print("Good bye!")
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