Python accumulative conditional logic

Question

I am struggling with the logic for the problem below and I know that even if I nailed the logic, I would probably implement it clumsily, so any advice would be awesome.

I have a dictionary representing a file:

the_file = {'Filename':'x:\\myfile.doc','Modified':datetime(2012,2,3),'Size':32412}

I have a list of filters and I want to filter the file dictionary to determine a match.

filters = [
    {'Key':'Filename','Criteria':'Contains','Value':'my'},
    {'Key':'Filename','Criteria':'Does not end with','Value':'-M.txt'},
    {'Key':'Modified','Criteria':'After','Value':datetime(2012,1,1)}
    ]

My best attempt at creating a function to do this (which doesn't work):

def is_asset(the_file, filters):
match = False
for f in filters:
    if f['Key'] == u'Filename':
        if f['Criteria'] == u'Contains':
            if f['Value'] in the_file['Filename']:
                match = True
        elif f['Criteria'] == u'Starts with':
            if the_file['Filename'].startswith(f['Value']):
                match = True
        elif f['Criteria'] == u'Ends with':
            if the_file['Filename'].endswith(f['Value']):
                match = True
        elif not f['Criteria'] == u'Does not end with':
            if the_file['Filename'].endswith(f['Value']):
                match = False
        elif f['Criteria'] == u'Equals':
            if os.path.basename(the_file['Filename']) == f['Value']:
                match = True
        elif f['Criteria'] == u'Does not contain':
            if f['Value'] in the_file['Filename']:
                match = False
    elif f['Key'] == u'Modified':
        mtime = int(os.path.getmtime(the_file['Filename']))
        if f['Criteria'] == u'Before':
            if f['Value'] > datetime.fromtimestamp(mtime):
                the_file['Modified'] = mtime
                match = True
        elif f['Criteria'] == u'After':
            if f['Value'] < datetime.fromtimestamp(mtime):
                the_file['Modified'] = mtime
                match = True
    elif f['Key'] == u'Size':
        size = long(os.path.getsize(the_file['Filename']))
        if f['Criteria'] == u'Bigger':
            if f['Value'] < size:
                the_file['Size'] = size
                match = True
            elif f['Value'] > size:
                the_file['Size'] = size
                match = True
    if match:
        return the_file

Ignacio Vazquez-Abrams · Accepted Answer · 2012-05-02 04:23:56Z

4

Instead of trying to do it in one megafunction, break it down into smaller steps.

filenamecondmap = {
  u'Contains': operator.contains,
  u'Does not end with': lambda x, y: not x.endswith(y),
   ...
}

 ...

condmap = {
  u'Filename': filenamecondmap,
  u'Modified': modifiedcondmap,
   ...
}

And then walk the structures until you have the conditional, then execute it.

condmap[u'Filename'][u'Contains'](thefile['Filename'], 'my')

answered May 2, 2012 at 4:23

Ignacio Vazquez-Abrams

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Comments

spinlok · Accepted Answer · 2012-05-02 04:34:35Z

2

You can simply use functions as your 'criteria'. This makes it much simpler, as you don't have to write a big if-else ladder. Something like this:

def contains(value, sub):
    return sub in value

def after(value, dt):
    return value > dt

filters = [
    {'Key': 'FileName', 'Criteria': contains, 'Value': 'my'},
    {'Key': 'Modified', 'Criteria': after,  'Value': datetime(2012,1,1)}
]

for f in filters:
    if f['Criteria'](filename[f['Key']], f['Value']):
       return True

answered May 2, 2012 at 4:34

spinlok

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1 Comment

MFB Over a year ago

I also learned a lot from your post, although I can only mark one answer. Thanks a lot.

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