Fixed error in infix2prefix file

DIRECTORY.md

@@ -101,6 +101,7 @@
   * [Decimal To Octal](https://github.com/TheAlgorithms/Python/blob/master/conversions/decimal_to_octal.py)
   * [Hexadecimal To Decimal](https://github.com/TheAlgorithms/Python/blob/master/conversions/hexadecimal_to_decimal.py)
   * [Molecular Chemistry](https://github.com/TheAlgorithms/Python/blob/master/conversions/molecular_chemistry.py)
+  * [Octal To Decimal](https://github.com/TheAlgorithms/Python/blob/master/conversions/octal_to_decimal.py)
   * [Prefix Conversions](https://github.com/TheAlgorithms/Python/blob/master/conversions/prefix_conversions.py)
   * [Roman To Integer](https://github.com/TheAlgorithms/Python/blob/master/conversions/roman_to_integer.py)
   * [Temperature Conversions](https://github.com/TheAlgorithms/Python/blob/master/conversions/temperature_conversions.py)
@@ -207,6 +208,7 @@
   * [Heaps Algorithm Iterative](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/heaps_algorithm_iterative.py)
   * [Inversions](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/inversions.py)
   * [Kth Order Statistic](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/kth_order_statistic.py)
+  * [Max Difference Pair](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/max_difference_pair.py)
   * [Max Subarray Sum](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/max_subarray_sum.py)
   * [Mergesort](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/mergesort.py)
   * [Peak](https://github.com/TheAlgorithms/Python/blob/master/divide_and_conquer/peak.py)
@@ -875,6 +877,8 @@
   * [Get Imdb Top 250 Movies Csv](https://github.com/TheAlgorithms/Python/blob/master/web_programming/get_imdb_top_250_movies_csv.py)
   * [Get Imdbtop](https://github.com/TheAlgorithms/Python/blob/master/web_programming/get_imdbtop.py)
   * [Instagram Crawler](https://github.com/TheAlgorithms/Python/blob/master/web_programming/instagram_crawler.py)
+  * [Instagram Pic](https://github.com/TheAlgorithms/Python/blob/master/web_programming/instagram_pic.py)
   * [Recaptcha Verification](https://github.com/TheAlgorithms/Python/blob/master/web_programming/recaptcha_verification.py)
   * [Slack Message](https://github.com/TheAlgorithms/Python/blob/master/web_programming/slack_message.py)
+  * [Test Fetch Github Info](https://github.com/TheAlgorithms/Python/blob/master/web_programming/test_fetch_github_info.py)
   * [World Covid19 Stats](https://github.com/TheAlgorithms/Python/blob/master/web_programming/world_covid19_stats.py)

data_structures/stacks/infix_to_prefix_conversion.py

@@ -1,7 +1,6 @@
 """
 Output:
-
-Enter an Infix Equation = a + b ^c
+Enter an infix Equation = a + b ^c
  Symbol  |  Stack  | Postfix
 ----------------------------
    c     |         | c
@@ -10,14 +9,13 @@
    +     | +       | cb^
    a     | +       | cb^a
          |         | cb^a+
-
-         a+b^c (Infix) ->  +a^bc (Prefix)
+         a+b^c (infix) ->  +a^bc (Prefix)
 """
 
 
-def infix_2_postfix(Infix):
-    Stack = []
-    Postfix = []
+def infix_2_postfix(infix):
+    stack = []
+    postfix = []
     priority = {
         "^": 3,
         "*": 2,
@@ -26,7 +24,7 @@ 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) if (len(infix) > 7) else 7
 
     # Print table header for output
     print(
@@ -37,57 +35,61 @@ def infix_2_postfix(Infix):
     )
     print("-" * (print_width * 3 + 7))
 
-    for x in Infix:
+    for x in infix:
         if x.isalpha() or x.isdigit():
-            Postfix.append(x)  # if x is Alphabet / Digit, add it to Postfix
+            postfix.append(x)  # if x is Alphabet / Digit, add it to postfix
         elif x == "(":
-            Stack.append(x)  # if x is "(" push to Stack
+            stack.append(x)  # if x is "(" push to stack
         elif x == ")":  # if x is ")" pop stack until "(" is encountered
-            while Stack[-1] != "(":
-                Postfix.append(Stack.pop())  # Pop stack & add the content to Postfix
-            Stack.pop()
+            while stack[-1] != "(":
+                postfix.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
+            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]]:
-                    Postfix.append(Stack.pop())  # pop stack & add to Postfix
-                Stack.append(x)  # push x to stack
+                while (
+                    len(stack) > 0
+                    and stack[-1] in priority
+                    and priority[x] <= priority[stack[-1]]
+                ):
+                    postfix.append(stack.pop())  # pop stack & add to postfix
+                stack.append(x)  # push x to stack
 
         print(
             x.center(8),
-            ("".join(Stack)).ljust(print_width),
-            ("".join(Postfix)).ljust(print_width),
+            ("".join(stack)).ljust(print_width),
+            ("".join(postfix)).ljust(print_width),
             sep=" | ",
         )  # Output in tabular format
 
-    while len(Stack) > 0:  # while stack is not empty
-        Postfix.append(Stack.pop())  # pop stack & add to Postfix
+    while len(stack) > 0:  # while stack is not empty
+        postfix.append(stack.pop())  # pop stack & add to postfix
         print(
             " ".center(8),
-            ("".join(Stack)).ljust(print_width),
-            ("".join(Postfix)).ljust(print_width),
+            ("".join(stack)).ljust(print_width),
+            ("".join(postfix)).ljust(print_width),
             sep=" | ",
         )  # Output in tabular format
 
-    return "".join(Postfix)  # return Postfix as str
+    return "".join(postfix)  # return postfix as str
 
 
-def infix_2_prefix(Infix):
-    Infix = list(Infix[::-1])  # reverse the infix equation
+def infix_2_prefix(infix):
+    infix = list(infix[::-1])  # reverse the infix equation
 
-    for i in range(len(Infix)):
-        if Infix[i] == "(":
-            Infix[i] = ")"  # change "(" to ")"
-        elif Infix[i] == ")":
-            Infix[i] = "("  # change ")" to "("
+    for i in range(len(infix)):
+        if infix[i] == "(":
+            infix[i] = ")"  # change "(" to ")"
+        elif infix[i] == ")":
+            infix[i] = "("  # change ")" to "("
 
-    return (infix_2_postfix("".join(Infix)))[
+    return (infix_2_postfix("".join(infix)))[
         ::-1
-    ]  # call infix_2_postfix on Infix, return reverse of Postfix
+    ]  # call infix_2_postfix on infix, return reverse of postfix
 
 
 if __name__ == "__main__":
-    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)")
+    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)")