added calculator.py

Author: shreydan

README.md

@@ -55,4 +55,4 @@ In the scripts the comments etc are lined up correctly when they are viewed in [
 
 - `timymodule.py` - A great alternative to Pythons 'timeit' module and easier to use.
 
-
+- `calculator.py` - Uses Python's eval() function to implement a calculator.

calculator.py

@@ -0,0 +1,40 @@
+"""
+Written by: Shreyas Daniel - github.com/shreydan
+Description: Uses Pythons infamous eval() function as a way to implement calculator
+"""
+
+import math
+
+
+def calc(k):
+
+    functions = ['sin','cos','tan','sqrt','pi']    
+    
+    
+    for i in functions:
+        if i in k.lower():
+            withmath = 'math.' + i
+            k = k.replace(i,withmath)
+    
+    try:
+        k = eval(k)
+    except ZeroDivisionError:
+        print ("Can't divide by 0")
+        exit()
+    except NameError:
+        print ("Invalid input")
+        exit()
+    
+    return k
+
+
+print ("\nScientific Calculator\nEg: pi * sin(90) - sqrt(81)")
+
+k = input("\nWhat is ")
+
+k = k.replace(' ','')
+k = k.replace('^','**')
+k = k.replace('=','')
+k = k.replace('?','')
+
+print ("\n" + str(calc(k)))