Add sign function to maths module

maths/sign.py

@@ -0,0 +1,40 @@
+"""Sign Function."""
+
+
+def sign(num: float) -> int:
+    """
+    Return the sign of a number: -1 for negative, 0 for zero, 1 for positive.
+
+    >>> sign(-5)
+    -1
+    >>> sign(0)
+    0
+    >>> sign(10)
+    1
+    >>> sign(-0.5)
+    -1
+    """
+    if num > 0:
+        return 1
+    elif num < 0:
+        return -1
+    return 0
+
+
+def test_sign():
+    """
+    >>> test_sign()
+    """
+    assert sign(-5) == -1
+    assert sign(0) == 0
+    assert sign(10) == 1
+    assert sign(-0.001) == -1
+    assert sign(0.001) == 1
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    test_sign()
+    print(sign(-5))  # --> -1