diff options
| author | Cengiz Kaygusuz <cngkaygusuz@gmail.com> | 2017-11-20 20:46:39 -0500 |
|---|---|---|
| committer | Cengiz Kaygusuz <cngkaygusuz@gmail.com> | 2017-11-20 20:46:39 -0500 |
| commit | 27e183a78c8062ed7c2bbb91655a5e56cd697bba (patch) | |
| tree | 88fd355a0cc6da4c130582e092d702836596cbb2 /examples/SimpleCalc.py | |
| parent | 4ba589cf13588e90992e23deb5a9784340efd2cc (diff) | |
| download | pyparsing-git-27e183a78c8062ed7c2bbb91655a5e56cd697bba.tar.gz | |
Move src to root
Diffstat (limited to 'examples/SimpleCalc.py')
| -rw-r--r-- | examples/SimpleCalc.py | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/examples/SimpleCalc.py b/examples/SimpleCalc.py new file mode 100644 index 0000000..46a5dff --- /dev/null +++ b/examples/SimpleCalc.py @@ -0,0 +1,118 @@ +# 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!")
+
+
|