Solution to problem 9 part 1 in Python

src/Year_2016/P9.py

@@ -0,0 +1,67 @@
+# --- Day 9: Explosives in Cyberspace ---
+
+# Wandering around a secure area, you come across a datalink port to a new part
+# of the network. After briefly scanning it for interesting files, you find one
+# file in particular that catches your attention. It's compressed with an
+# experimental format, but fortunately, the documentation for the format is
+# nearby.
+
+# The format compresses a sequence of characters. Whitespace is ignored. To
+# indicate that some sequence should be repeated, a marker is added to the
+# file, like (10x2). To decompress this marker, take the subsequent 10
+# characters and repeat them 2 times. Then, continue reading the file after the
+# repeated data. The marker itself is not included in the decompressed output.
+
+# If parentheses or other characters appear within the data referenced by a
+# marker, that's okay - treat it like normal data, not a marker, and then
+# resume looking for markers after the decompressed section.
+
+# For example:
+
+#     ADVENT contains no markers and decompresses to itself with no changes,
+# resulting in a decompressed length of 6.
+#     A(1x5)BC repeats only the B a total of 5 times, becoming ABBBBBC for a
+# decompressed length of 7.
+#     (3x3)XYZ becomes XYZXYZXYZ for a decompressed length of 9.
+#     A(2x2)BCD(2x2)EFG doubles the BC and EF, becoming ABCBCDEFEFG for a
+# decompressed length of 11.
+#     (6x1)(1x3)A simply becomes (1x3)A - the (1x3) looks like a marker, but
+# because it's within a data section of another marker, it is not treated any
+# differently from the A that comes after it. It has a decompressed length of
+# 6.
+#     X(8x2)(3x3)ABCY becomes X(3x3)ABC(3x3)ABCY (for a decompressed length of
+# 18), because the decompressed data from the (8x2) marker (the (3x3)ABC) is
+# skipped and not processed further.
+
+# What is the decompressed length of the file (your puzzle input)? Don't count
+# whitespace.
+
+import re
+
+with open("files/P9.txt") as f:
+    chars = [line for line in f.read().strip().split()]
+
+
+def recursive_decompression(my_str):
+    marker = re.search(r"\(\d+x\d+\)", my_str)
+
+    if not marker:
+        return my_str
+    else:
+        markers = re.findall(r"\d+", marker.group())
+        chars_to_repeat, times = (int(n) for n in markers)
+        start, end = marker.start(), marker.end()
+        return (
+            my_str[:start]
+            + times * my_str[end : end + chars_to_repeat]
+            + recursive_decompression(my_str[end + chars_to_repeat :])
+        )
+
+
+def part_1() -> None:
+    ans = len(recursive_decompression(chars[0]))
+    print(f"The length of the file is {ans}")
+
+
+if __name__ == "__main__":
+    part_1()