how to do something with the output of a function, which is a dictionary?

Question

Can anyone help me with the following problem? I have a previous function that returns a dictionary. Now I need this function to make a new one, but I need to do something with the dictionary. To show you what I'm trying to do, dictionary(fasta_filename) is my previous function;

def test(fasta_filename, minMW, maxMW):
    interval = minMW, maxMW
    for key, value in dictionary(fasta_filename).items():
        if value in interval:
            print(key)
        else:
            print('intervals do not match')

This is just starting to try what I want to do, but the main problem I have is that the things you can do with a dictionary, like the .items(), are not working if you try to do it on the function. The error says: 'NoneType' object has no attribute 'items'. I understand this error, because when you do function.items() you assume the function IS the dictionary, but it's not. I'm still very new to all this, perhaps you can tell, but I would appreciate it if someone could give me a hint. :)

There are some problems here: (a) by `value in interval`, you do not check a value against an interval, but check if a value is either `minMW` or `maxMW`. Furthermore this function does *not* provide output, it `print`s things, which is I/O. You `return` things with the `return` keyword. — Willem Van Onsem, Dec 30 '17 at 21:17
Your `dictionary` function is returning `None` at least some times, in which case `dictionary(fasta_filename).items()` will not work, but it *would* work if your function in fact returned a `dict` object. Without seeing the `dictionary` function, I can only speculate. — juanpa.arrivillaga, Dec 30 '17 at 21:19
Note, you aren't doing `function.items()`, which would be `dictionary.items()`, that error would be slightly different, it would say `AttributeError: 'function' object has no attribute 'items'`, but in your case, it is `"'NoneType' object has no attribute 'items'"`. Since you correctly *call* the function, i.e. `dictionary(...)` — juanpa.arrivillaga, Dec 30 '17 at 21:23

Patrick Artner · Answer 1 · 2017-12-30T21:29:52.237

You could fix your testing like this, but it still will only print stuff out.

Modify the return statement of the def dictionary(fn) function to check the different outputs for a None-dict and a dict that contains data and is checked.

def dictionary(fn):
    # you do stuff here with your file, make sure to NOT return None but 
    # always retunr at least an empty dict if your actions on your file 
    # do not result in a filled dictionary
    return {"dummy1" : 55, "dummy2" : 97, "dummy3" : 12345}
    # return None # uncomment this and comment the one above for a None-Dict

def test(fasta_filename, minMW, maxMW):
    interval = range(minMW, maxMW+1) # this is the interval [minMW..maxMW] including both
    dic = dictionary(fasta_filename)
    if not dic:
        print('dictionary is None')
        return None # leave test method

    for key, value in dic.items():
        if value in interval:
            print(key)
        else:
            print('intervals do not match for', key)

test("does not matter, dummy data provided internally",60,120)

Output (python 3.6):

intervals do not match for dummy1
dummy2
intervals do not match for dummy3

or

dictionary is None

depending on what def dictionary(fn) returns.

Thank you, I understand the difference between return and print better now! I how have a function, and it works, but only for the not matching intervals. I thought it was because the output of the dictionary, which is like this: {'seq_7009': (6236.9764, 6367.049999999999), 'seq_418': (3716.3642000000004, 3796.4124000000006), ...)} did not work for the interval because of the floating point numbers. I tried adding a step in the range like 'interval = range(minMW, maxMW+1, 0.00000000001)' but then it says: 'TypeError: 'float' object cannot be interpreted as an integer'. — Jozefien Demuynck, Jan 02 '18 at 12:50

how to do something with the output of a function, which is a dictionary?

1 Answers1