Adding a constant integer to a value in a python dictionary

Question

How would you add a constant number, say 1, to a value in a dictionary if certain conditions are fulfilled.

For example, if I had a dictionary:

dict          


        

Answer 1

Another way of doing this would be to use the items() method of dictionary which returns a list of key, value tuples:

def f(dict):
    for entry in dict.items():
        if entry[1] > 1 and entry[1] < 5:
            dict[entry[0]] = entry[1] + 1
    return dict

You can then extend this to take an arbitrary function:

def f(dict, func):
    for entry in dict.items():
        if func(entry[1]):
            dict[entry[0]] = entry[1] + 1
    return dict

This can be provided a function such as:

def is_greater_than_one(x):
    return x > 1

and called in the following way:

f(input_dictionary,is_greater_than_one)

Answer 2

One simple way to do this is to use a collections.Counter object, which you can use in every way like a normal dictionary in most ways but it is optimized for keeping a count of items:

>>> from collections import Counter
>>> d = Counter({'0':3, '1':3, '2':4, '3':4, '4':4})
>>> d
Counter({'3': 4, '2': 4, '4': 4, '1': 3, '0': 3})
>>> d.update(d.keys())
>>> d
Counter({'3': 5, '2': 5, '4': 5, '1': 4, '0': 4})

As for only doing it when certain conditions are fulfilled, just use a comprehension or generator to only pass the list of the keys you want to increment to d.update():

>>> d = Counter({'3': 4, '2': 4, '4': 4, '1': 3, '0': 3})
>>> d.update((k for k, v in d.items() if v == 4))
>>> d
Counter({'3': 5, '2': 5, '4': 5, '1': 3, '0': 3})

Answer 3

Your code says the following:

for each value in [3,3,4,4,4]:
    if 1 < value < 5:
        FID_thingy['0'] = value + 1

So it will set FID_thingy['0'] to 4 then 4 then 5 then 5 then 5. Do you see why?