Solution 076 LK Task 1 Python

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+#!/usr/bin/env python
+""" Perl weekly challenge 076 """
+# ===============================================================================
+#
+#         FILE: ch-1.py
+#
+#        USAGE: ./ch-1.py
+#
+#  DESCRIPTION: https://perlweeklychallenge.org/blog/perl-weekly-challenge-076/
+#
+#              Task 1 - Prime Sum
+#
+#       AUTHOR: Lubos Kolouch
+# ===============================================================================
+from sympy import isprime
+
+
+def get_nr_primes(what):
+    """ Calculate and return the number of primes needed """
+
+    # if the number is prime, we need just 1 number to represent it
+
+    if isprime(what):
+        return 1
+
+    # if the number is even, we need 2 primes thanks to Goldbach's conjecture
+    if what % 2 == 1:
+        return 2
+
+    # if the number - 2 is prime, return 2
+    if isprime(what - 2):
+        return 2
+
+    # if the number -3 is prime, return 2 (3 and the prime)
+    if isprime(what - 3):
+        return 2
+
+    # otherwise return 3 - it is 3 and 2 primes forming $what - 3 thanks to
+    # Goldbach's conjecture
+    return 3
+
+
+assert get_nr_primes(2) == 1
+assert get_nr_primes(9) == 2
+assert get_nr_primes(10) == 2
+assert get_nr_primes(12) == 3