refactor: simplify character filtering in is_pangram

Refactored is_pangram function to use isalpha for letter check and removed benchmark function.

Author: Tithi234

strings/is_pangram.py

@@ -21,13 +21,10 @@ def is_pangram(
     >>> is_pangram()
     True
     """
-    # Declare frequency as a set to have unique occurrences of letters
     frequency = set()
-
-    # Replace all the whitespace in our sentence
     input_str = input_str.replace(" ", "")
     for alpha in input_str:
-        if "a" <= alpha.lower() <= "z":
+        if alpha.isalpha():
             frequency.add(alpha.lower())
     return len(frequency) == 26
 
@@ -73,23 +70,6 @@ def is_pangram_fastest(
     """
     return len({char for char in input_str.lower() if char.isalpha()}) == 26
 
-
-def benchmark() -> None:
-    """
-    Benchmark code comparing different version.
-    """
-    from timeit import timeit
-
-    setup = "from __main__ import is_pangram, is_pangram_faster, is_pangram_fastest"
-    print(timeit("is_pangram()", setup=setup))
-    print(timeit("is_pangram_faster()", setup=setup))
-    print(timeit("is_pangram_fastest()", setup=setup))
-    # 5.348480500048026, 2.6477354579837993, 1.8470395830227062
-    # 5.036091582966037, 2.644472333951853,  1.8869528750656173
-
-
-if __name__ == "__main__":
-    import doctest
-
-    doctest.testmod()
-    benchmark()
+   
+    
+