Python Regular Expressions implement the calculator function, python Regular Expressions

Python Regular Expressions implement the calculator function, python Regular Expressions

Requirements:

The user enters an operation expression and the terminal displays the calculation result.

Code:

#! /Usr/bin/env/python3 #-*-coding: UTF-8-*-"the user inputs the computation expression, show the calculation result "" _ author _ = 'jack' import rebracket = re. compile (R' \ ([^ ()] + \) ') # Find the inmost bracket rule mul = re. compile (R' (\ d + \.? \ D * \ *-\ d + \.? \ D *) | (\ d + \.? \ D * \ d + \.? \ D *) ') # Find the multiplication rule div = re. compile (R' (\ d ++ \.? \ D */-\ d + \.? \ D *) | (\ d + \.? \ D */\ d + \.? \ D *) ') # search for the Division rule add = re. compile (R '(-? \ D + \.? \ D * \ +-\ d + \.? \ D *) | (-? \ D + \.? \ D * \ + \ d + \.? \ D *) ') # search for addition operation rules sub = re. compile (R' (\ d ++ \.? \ D * -- \ d + \.? \ D *) | (\ d + \.? \ D *-\ d + \.? \ D *) ') # search for the subtraction rule c_f = re. compile (R '\(? \ +? -? \ D ++ \)? ') # Check whether the rule strip = re. compile (R' [^ (]. * [^)] ') # detachment rule def Mul (s): "Multiplication operation in calculation expression" exp = re. split (R' \ * ', mul. search (s ). group () return s. replace (mul. search (s ). group (), str (float (exp [0]) * float (exp [1]) def Div (s ): "division operation in calculation expression" "exp = re. split (R'/', div. search (s ). group () return s. replace (div. search (s ). group (), str (float (exp [0])/float (exp [1]) def Add (s ): "addition operation in calculation expression" "exp = re. split (R' \ + ', add. search (s ). group () return s. replace (add. search (s ). group (), str (float (exp [0]) + float (exp [1]) def Sub (s ): "subtraction operation in calculation expression" "exp = re. split (R'-', sub. search (s ). group () return s. replace (sub. search (s ). group (), str (float (exp [0])-float (exp [1]) def calc (): while True: s = input ('Please input the expression (q for quit): ') # example: '1 + 2-(3*4-3/2 + (3-2*(3 + 5-3 *-0.2-3.3*2.2-8.5/2.4) + 10) + 10) 'if s = 'q': break else: s = ''. join ([x for x in re. split ('\ s +', s)]) # split the expression by space and restructure if not s. startswith ('): # if there are no parentheses at the beginning and end of the expression entered by the user, the format is: (expression) s = str (' (% s) '% s) while bracket. search (s): # If expression s contains brackets s = s. replace ('--', '+') # Check the expression and replace the -- operation with the + operation s_search = bracket. search (s ). group () # assign the inner brackets and content to the variable s_search if div. search (s_search): # If the division operation exists (must be placed before multiplication) s = s. replace (s_search, Div (s_search) # execute the division operation and replace the result with the original expression elif mul. search (s_search): # If multiplication exists, s = s. replace (s_search, Mul (s_search) # execute the multiplication operation and replace the result with the original expression elif sub. search (s_search): # If the subtraction operation exists (must be placed before addition) s = s. replace (s_search, Sub (s_search) # execute the subtraction operation and replace the result with the original expression elif add. search (s_search): # If the addition operation has s = s. replace (s_search, Add (s_search) # execute the addition operation and replace the result with the original expression elif c_f.search (s_search): # If no operation is performed in the brackets (similar to (-2.32) s = s. replace (s_search, strip. search (s_search ). group () # Remove The parentheses, for example: (-2.32) --->-2.32 print ('The answer is: %. 2f '% (float (s) if _ name _ =' _ main _ ': calc ()

Running effect:

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