Add default args and type hints for problem 7 (#2973)

- Add default argument values
- Add type hints
- Change one letter variable names to a more descriptive one
- Add doctest for `solution()`

project_euler/problem_07/sol1.py

@@ -1,4 +1,6 @@
 """
+Problem 7: https://projecteuler.net/problem=7
+
 By listing the first six prime numbers:
 
     2, 3, 5, 7, 11, and 13
@@ -8,20 +10,21 @@ We can see that the 6th prime is 13. What is the Nth prime number?
 from math import sqrt
 
 
-def is_prime(n):
-    if n == 2:
+def is_prime(num: int) -> bool:
+    """Determines whether the given number is prime or not"""
+    if num == 2:
         return True
-    elif n % 2 == 0:
+    elif num % 2 == 0:
         return False
     else:
-        sq = int(sqrt(n)) + 1
+        sq = int(sqrt(num)) + 1
         for i in range(3, sq, 2):
-            if n % i == 0:
+            if num % i == 0:
                 return False
     return True
 
 
-def solution(n):
+def solution(nth: int = 10001) -> int:
     """Returns the n-th prime number.
 
     >>> solution(6)
@@ -36,18 +39,20 @@ def solution(n):
     229
     >>> solution(100)
     541
+    >>> solution()
+    104743
     """
-    i = 0
-    j = 1
-    while i != n and j < 3:
-        j += 1
-        if is_prime(j):
-            i += 1
-    while i != n:
-        j += 2
-        if is_prime(j):
-            i += 1
-    return j
+    count = 0
+    number = 1
+    while count != nth and number < 3:
+        number += 1
+        if is_prime(number):
+            count += 1
+    while count != nth:
+        number += 2
+        if is_prime(number):
+            count += 1
+    return number
 
 
 if __name__ == "__main__":