# Writing data files in the simulation output directory.¶

Quite often when you run CC3D simulations you need to output data files where you store some information about the simulation. When CC3D saves simulation snapshots it does so in the special directory which is created automatically and whose name consists of simulation core name and timestamp. By default, CC3D creates such directories as subfolders of <your_home_directory>/CC3DWorkspace. You can redefine the location of CC3D output in the Player or from the command line. If standard simulation output is placed in a special directory it makes a lot of sense to store your custom data files in the same directory. The following code snippet shows you how to accomplish this (the code to open file in the simulation output directory can be inserted from Twedit++ - simply go to CC3D Python->Python Utilities):

def step(self, mcs):

output_dir = self.output_dir

if output_dir is not None:
output_path = Path(output_dir).joinpath('step_' + str(mcs).zfill(3) + '.dat')
with open(output_path, 'w') as fout:

attr_field = self.field.ATTR
for x, y, z in self.every_pixel():
fout.write('{} {} {} {}\n'.format(x, y, z, attr_field[x, y, z]))


In the step function we create output_path by concatenating output_dir with a string that contains word step_ , current mcs (zero-filled up to 3 positions - note how we use standard string function zfill) and extension .dat

Note

self.output_dir is a special variable in each steppable that stores directory where the output

of the current simulation will be written.

Note

Path concatenation in Path(output_dir).joinpath(...) is done using standard Python package pathlib. we import this functionality using from pathlib import Path

Next, we open file using with statement - if you are unfamiliar with this way of interacting with files in Python
please check new Python tutorials online:
with open(output_path, 'w') as fout:
# file is open at this point and there is no need to close it
# because "with" statement will take care of it automatically
...


Inside with statement (where the file is open) we access chemical field ATTR and use self.every_pixel operator to access and write field values to the file:

with open(output_path, 'w') as fout:

attr_field = self.field.ATTR
for x, y, z in self.every_pixel():
fout.write('{} {} {} {}\n'.format(x, y, z, attr_field[x, y, z]))


If we want to create directory inside simulaiton output folder we can use the following functionality of pathlib

new_dir = Path(self.output_dir).joinpath('new_dir/new_subdir')
new_dir.mkdir(exist_ok=True, parents=True)


We first create path to the new directory using pathlib’s Path object and its joinpath method. and then use Path’s method mkdir to create directory. The exist_ok=True, parents=True arguments ensure that the function will not crash if the directory already exists and all the paths along directory path will be created as needed (parents=True). In our case it means that new_dir and new_subdir will be created. self.output_dir will be created as well but in a different place by the CC3D simulation setup code.