Added doctests, exceptions, type hints, fixed bug for infix_to_prefix_conversion

data_structures/stacks/infix_to_prefix_conversion.py

@@ -15,7 +15,7 @@
 """
 
 
-def infix_2_postfix(infix):
+def infix_2_postfix(infix: list[str]) -> str:
  stack = []
  post_fix = []
  priority = {
@@ -26,7 +26,8 @@ def infix_2_postfix(infix):
  "+": 1,
  "-": 1,
  } # Priority of each operator
- print_width = len(infix) if (len(infix) > 7) else 7
+
+ print_width = len(infix)
 
  # Print table header for output
  print(
@@ -43,14 +44,21 @@ def infix_2_postfix(infix):
  elif x == "(":
  stack.append(x) # if x is "(" push to Stack
  elif x == ")": # if x is ")" pop stack until "(" is encountered
+ if len(stack) == 0: # close bracket without open bracket
+ raise ValueError("Invalid bracket position(s)")
+
  while stack[-1] != "(":
  post_fix.append(stack.pop()) # Pop stack & add the content to Postfix
  stack.pop()
  else:
  if len(stack) == 0:
  stack.append(x) # If stack is empty, push x to stack
  else: # while priority of x is not > priority of element in the stack
- while len(stack) > 0 and priority[x] <= priority[stack[-1]]:
+ while (
+ len(stack) > 0
+ and stack[-1] != "("
+ and priority[x] <= priority[stack[-1]]
+ ):
  post_fix.append(stack.pop()) # pop stack & add to Postfix
  stack.append(x) # push x to stack
 
@@ -62,6 +70,9 @@ def infix_2_postfix(infix):
  ) # Output in tabular format
 
  while len(stack) > 0: # while stack is not empty
+ if stack[-1] == "(": # open bracket with no close bracket
+ raise ValueError("Invalid bracket position(s)")
+
  post_fix.append(stack.pop()) # pop stack & add to Postfix
  print(
  " ".center(8),
@@ -73,7 +84,52 @@ def infix_2_postfix(infix):
  return "".join(post_fix) # return Postfix as str
 
 
-def infix_2_prefix(infix):
+def infix_2_prefix(infix: str) -> str:
+ """
+ >>> infix_2_prefix('a+b^c')
+ Symbol | Stack | Postfix
+ ----------------------------
+ c | | c
+ ^ | ^ | c
+ b | ^ | cb
+ + | + | cb^
+ a | + | cb^a
+ | | cb^a+
+ '+a^bc'
+
+ >>> infix_2_prefix('1*((-a)*2+b)')
+ Symbol | Stack | Postfix
+ -------------------------------------------
+ ( | ( |
+ b | ( | b
+ + | (+ | b
+ 2 | (+ | b2
+ * | (+* | b2
+ ( | (+*( | b2
+ a | (+*( | b2a
+ - | (+*(- | b2a
+ ) | (+* | b2a-
+ ) | | b2a-*+
+ * | * | b2a-*+
+ 1 | * | b2a-*+1
+ | | b2a-*+1*
+ '*1+*-a2b'
+
+ >>> infix_2_prefix('')
+ Symbol | Stack | Postfix
+ ----------------------------
+ ''
+
+ >>> infix_2_prefix('(()')
+ Traceback (most recent call last):
+ ...
+ ValueError: Invalid bracket position(s)
+
+ >>> infix_2_prefix('())')
+ Traceback (most recent call last):
+ ...
+ ValueError: Invalid bracket position(s)
+ """
  infix = list(infix[::-1]) # reverse the infix equation
 
  for i in range(len(infix)):
@@ -88,6 +144,10 @@ def infix_2_prefix(infix):
 
 
 if __name__ == "__main__":
+ from doctest import testmod
+
+ testmod()
+
  Infix = input("\nEnter an Infix Equation = ") # Input an Infix equation
  Infix = "".join(Infix.split()) # Remove spaces from the input
  print("\n\t", Infix, "(Infix) -> ", infix_2_prefix(Infix), "(Prefix)")