# Project Euler module

I use Project Euler to teach me programming and not to submit any results. As such I look up the expected return values to double check my solutions.

To organise my files I use the following folder structure:

main.py
\euler # The problem files
__init__.py # empty
e001.py
e002.py
...
8.dat
11.dat
...


My main.py file is the common entry point. It can either run all the solved examples so far or a specific one. This second option is added that I don't need to add an if __name__ == '__main__' guard in every file. The file looks as follows:

TOP_LEVEL = "euler"

def run_module(num):
"""Run specific Problem"""
mod = importlib.import_module('%s.e%0.3i' % (TOP_LEVEL, num))

start = time.time()
ist = mod.run()
print("  %5i | %6.3f |  %s  | %i" % \
(num, time.time() - start, "ox"[ist == mod.SOLL], ist))

if __name__ == '__main__':
N_MAX = 67

print('Problem |  Time  | x/o | Solution')
print("--------+--------+-----+---------")

global_time = time.time()

# Run over all problems
if len(sys.argv) == 2:
run_module(int(sys.argv[1]))
else:
for num in range(1, N_MAX + 1):
run_module(num)

print("--------+--------+-----+---------")
print("Total: %.3f s" % (time.time() - global_time))


I'll show now two example files to show the source files and how old code can be reused. e018.py:

"""By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum total from top to bottom is 23.

3
7 4
2 4 6
8 5 9 3
That is, 3 + 7 + 4 + 9 = 23.

Find the maximum total from top to bottom of the triangle below"""

SOLL = 1074

def run(file = "input/18.dat"):
# Parse File
with open(file) as fid:
tri = [[int(num) for num in line.split(' ')] for line in fid.read().split('\n')]

# From bottom's up find the maximal value
for row in range(len(tri) - 2, -1, -1):
for col in range(row + 1):
tri[row][col] += max(tri[row + 1][col], tri[row + 1][col + 1])

return tri[0][0]


and e067.py

"""By starting at the top of the triangle below and moving to adjacent numbers on the row below, the maximum total from top to bottom is 23.

3
7 4
2 4 6
8 5 9 3
That is, 3 + 7 + 4 + 9 = 23.

Find the maximum total from top to bottom of the triangle below"""

import e018

SOLL = 7273

def run(file = "input/67.dat"):
# problem has been solved in set 18
return e018.run(file = file)


Since this is the first time I tried to structure such a project, I'm quite sure there is plenty of room for optimization. I'm happy for any feedback I can get.

Use .format

Using % is considered old style, so:

print("  %5i | %6.3f |  %s  | %i".format(
(num, time.time() - start, "ox"[ist == mod.SOLL], ist)))


Be generous with long variables names

For example ist is impossible to understand for me, solution is more natural

Don't abuse Code-Golf techniques

The line:

"ox"[ist == mod.SOLL]


is a well known Code-Golf trick that relies on implicit boolean to integer conversion that is equivalent to:

"x" if ist == mod.SOLL else "o"


Use argparse

C-Style arguments such as sys.argv[1] should be avoided, I suggest argparse (help to get started here: https://stackoverflow.com/questions/7427101/dead-simple-argparse-example-wanted-1-argument-3-results)

def run(file = "input/18.dat"):
# Parse File
with open(file) as fid:


file is a built-in, you should use file_ in your code.

Explode long lines

Divide the following lines in two please.

 tri = [[int(num) for num in line.split(' ')] for line in fid.read().split('\n')]

• Thank you for this input. I definitely have to look into the .format since I still stick to c formatting all the time. I also started using argparse meanwhile and learned to like it. Once thing I'm myself not really certain about is the shadowing of the file variable. A better name might have been path anyway but is it really so bad to shadow a builtin for which nearly nobody is ever gonna call its constructor directly? Conserning the data structure I was also wondering if you had any input about that. – magu_ Jun 15 '15 at 16:18
• @magu_ it is better not to, because, for example in an IDE file will change colour, and seeing an ordinary variable of another colour is distracting – Caridorc Jun 15 '15 at 16:19
• Yes, I guess your right. – magu_ Jun 15 '15 at 18:32