Create hexadecimal_to_decimal

conversions/hexadecimal_to_decimal

@@ -0,0 +1,45 @@
+hex_table = {hex(i)[2:]: i for i in range(16)}  # Use [:2] to strip off the leading '0x'
+
+
+def hex_to_decimal(hex_string: str) -> int:
+    """
+    Convert a hexadecimal value to its decimal equivalent
+    #https://www.programiz.com/python-programming/methods/built-in/hex
+
+    >>> hex_to_decimal("a")
+    10
+    >>> hex_to_decimal("12f")
+    303
+    >>> hex_to_decimal("   12f   ")
+    303
+    >>> hex_to_decimal("FfFf")
+    65535
+    >>> hex_to_decimal("-Ff")
+    -255
+    >>> hex_to_decimal("F-f")
+    ValueError: Non-hexadecimal value was passed to the function
+    >>> hex_to_decimal("")
+    ValueError: Empty string value was passed to the function
+    >>> hex_to_decimal("12m")
+    ValueError: Non-hexadecimal value was passed to the function
+    """
+    hex_string = hex_string.strip().lower()
+    if not hex_string: 
+        raise ValueError("Empty string was passed to the function")
+    is_negative = hex_string[0] == "-"
+    if is_negative:
+        hex_string = hex_string[1:]
+    if not all(char in hex_table for char in hex_string):
+        raise ValueError("Non-hexadecimal value was passed to the function")
+    decimal_number = 0
+    for char in hex_string:
+        decimal_number = 16 * decimal_number + hex_table[char]
+    if is_negative:
+        decimal_number = -decimal_number
+    return decimal_number
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()