# AoC 2017: Library Functions

As mentioned in the main post, I’m structuring my solutions a bit differently this year. Rather than repeating the same relatively lengthy header in each function, we’re going to have a few shared files that can be imported or used for every problem.

Specifically, I have a trio of shared files not directly related to any particular day:

• lib.py - a shared library that can be used my multiple files; this will handle command line parameters, user input from files, logging, and have a few helper functions

To start out with, we have the a few basic parameters that are available to any day:

_arg_parser = argparse.ArgumentParser()
_arg_parser.add_argument('--part', type = int, default = 1, choices = (1, 2))

_argument_groups = {}

_DEBUG_MODE = False

def param(name, cache = {}):
'''
Get parameters from the command line by name.
arg('input') will generate lines of input from fileinput
'''

global _DEBUG_MODE

if not cache:
cache['args'], cache['unknown'] = _arg_parser.parse_known_args()

if cache['args'].debug:
_DEBUG_MODE = True

if name == 'input' and not hasattr(cache['args'], 'input'):
return fileinput.input(cache['unknown'])
else:
return getattr(cache['args'], name)

Mostly, this wraps argparse , but it also lets us get parameters without having to worry about the underlying implementation. In addition, we can use this for logging:

def log(message, *args, **kwargs):
if _DEBUG_MODE:
print(message.format(*args, **kwargs))

This is faster than Python’s built in logging function since it doesn’t even try to log if we’re not in _DEBUG_MODE.

Next, we have a standard lib.input() function that will automatically wrap fileinput . That’s a nice library that will make Unix style file input easy. You can either read from stdin without specifying anything, or you can can specify one or more files to read from instead. This is all handled automatically, including stripping all whitespace / just newlines and skipping (Python style) comments. All a specific day has to do is something akin to for line in lib.input().

Last but not least (there will be more in specific days), I have a general math function:

def math(expression, variables):
'''Safely evaluate a mathematical expression with the given variables.'''

if re.match(r'[^0-9a-z+\-*/ ]', expression):
raise Exception('Unsafe expression: {}'.format(expression))

# TODO: Make this actually safe.

return eval(expression, globals(), variables)

This will ‘safely’ evaluate a basic mathematical expression. It can only contain numbers, variable names, and the four basic operators (+, -, *, /), but it’s useful from time to time to be able to evaluate mathematical expressions. It came up a few times last year.

The only remaining annoyance I have is that it’s not super easy to import a Python file from one level above where you are running. I finally settled on this:

import sys; sys.path.insert(0, '..'); import lib

It’s ugly, but it works. Perhaps I’ll figure out something more elegant in the future? Running from one level up would work, but that’s not something I want to do just yet.

Next up, we have something like a test suite:

• test-cases.yaml - a list of commands that can be run to print out my particular answers for every day along with timing information
• run-all.py - the script that actually loads test-cases.yaml and runs it

That will let me run either specific days:

$python3 run-all.py day-01 day-01 python3 ahctpat.py input.txt 0.05250382423400879 1102 day-01 python3 ahctpat.py input.txt --function "size // 2" 0.055709123611450195 1076 Or everything: $ python3 run-all.py

day-01  python3 ahctpat.py input.txt    0.05324125289916992     1102
day-01  python3 ahctpat.py input.txt --function "size // 2"     0.05552506446838379     1076
day-02  python3 check-it.py input.txt --part 1  0.05425620079040527     51139
day-02  python3 check-it.py input.txt --part 2  0.05429983139038086     272
day-03  python3 spiraly.py 347991 --part 1      0.5735530853271484      480
day-03  python3 spiraly.py 347991 --part 2      0.06040596961975098     349975
day-04  python3 password-validator.py input.txt 0.059782981872558594    337
day-04  python3 password-validator.py input.txt --no-anagrams   0.06075477600097656     231
...

It gives me the day, the command I ran, how long it took to run (in seconds), and the output I would submit to solve the puzzle. It’s nice to have it all in one place.

And… that’s about it for now.