As others have stated, you usually want to be doing runtime class generation for this kind of thing, rather than creating individual files.
But I thought: what if you had some good reason to do this, like just making class templates for a bunch of files, so that you could go in and expand them later? Say I plan on writing a lot of code, so I'd like to automate the boilerplate code parts, that way I'm not stuck doing tedious work.
Turns out writing a simple templating engine for Python classes isn't that hard. Here's my go at it, which is able to do templating from a csv file.
from os import path
from sys import argv
import csv
INIT = 'def __init__'
def csvformat(csvpath):
""" Read a csv file containing a class name and attrs.
Returns a list of the form [['ClassName', {'attr':'val'}]].
"""
csv_lines = []
with open(csvpath) as f:
reader = csv.reader(f)
_ = [csv_lines.append(line)
for line in reader]
result = []
for line in csv_lines:
attr_dict = {}
attrs = line[1:]
last_attr = attrs[0]
for attr in attrs[1:]:
if last_attr:
attr_dict[last_attr] = attr
last_attr = ''
else:
last_attr = attr
result.append([line[0], attr_dict])
return result
def attr_template(attrs):
""" Format a list of default attribute setting code. """
attr_list = []
for attr, val in attrs.items():
attr_list.append(str.format(' if {} is None:\n', attr, val))
attr_list.append(str.format(' self.{} = {}\n', attr, val))
attr_list.append(' else:\n')
attr_list.append(str.format(' self.{} = {}\n', attr, attr))
return attr_list
def import_template(imports):
""" Import superclasses.
Assumes the .py files are named based on the lowercased class name.
"""
imp_lines = []
for imp in imports:
imp_lines.append(str.format('from {} import {}\n',
imp.lower(), imp))
return imp_lines
def init_template(attrs):
""" Template a series of optional arguments based on a dict of attrs.
"""
init_string = 'self'
for key in attrs:
init_string += str.format(', {}=None', key)
return init_string
def gen_code(foldername, superclass, name, attrs):
""" Generate python code in foldername.
Uses superclass for the superclass, name for the class name,
and attrs as a dict of {attr:val} for the generated class.
Writes to a file with lowercased name as the name of the class.
"""
imports = [superclass]
pathname = path.join(foldername, name.lower() + '.py')
with open(pathname, 'w') as pyfile:
_ = [pyfile.write(imp)
for imp
in import_template(imports)]
pyfile.write('\n')
pyfile.write((str.format('class {}({}):\n', name, superclass)))
pyfile.write((str.format(' {}({}):\n',
INIT, init_template(attrs))))
_ = [pyfile.write(attribute)
for attribute
in attr_template(attrs)]
pyfile.write(' super().__init__()')
def read_and_generate(csvpath, foldername, superclass):
class_info = csvformat(csvpath)
for line in class_info:
gen_code(foldername, superclass, *line)
def main():
read_and_generate(argv[1], argv[2], argv[3])
if __name__ == "__main__":
main()
The above takes a csvfile formatted like this as its first argument (here, saved as a.csv):
Magistrate,foo,42,fizz,'baz'
King,fizz,'baz'
Where the first field is the class name, followed by the attribute name and its default value. The second argument is the path to the output folder.
If I make a folder called classes and create a classes/mysuper.py in it with a basic class structure:
class MySuper():
def __init__(*args, **kwargs):
pass
And then run the code like this:
$ python3 codegen.py a.csv classes MySuper
I get the files classes/magistrate.py with the following contents:
from mysuper import MySuper
class Magistrate(MySuper):
def __init__(self, fizz=None, foo=None):
if fizz is None:
self.fizz = 'baz'
else:
self.fizz = fizz
if foo is None:
self.foo = 42
else:
self.foo = foo
super().__init__()
And classes/king.py:
from mysuper import MySuper
class King(MySuper):
def __init__(self, fizz=None):
if fizz is None:
self.fizz = 'baz'
else:
self.fizz = fizz
super().__init__()
You can actually load them and use them, too!
$ cd classes
classes$ python3 -i magistrate.py
>>> m = Magistrate()
>>> m.foo
42
>>> m.fizz
'baz'
>>>
The above generates Python 3 code, which is what I'm used to, so you will need to make some small changes for it to work in Python 2.
