CODEWITHSUNDEEP
pythondictionary
Ajay
Ajay

Reputation: 407

Properly looping over a dictionary / using dictionaries as databases

This looks like a CS 101 style homework but it actually isn't. I am trying to learn more python so I took up this personal project to write a small app that keeps my grade-book for me.

I have a class semester which holds a dictionary of section objects. A section is a class that I am teaching in which ever semester object I am manipulating (I didn't want to call them classes for obvious reasons). I originally had sections as a list not a dictionary, and when I wanted to add a roster of students to that semester I could do this.

for sec in working_semester.sections:
    sec.addRosterFromFile(filename)

Now I have changed the sections member of semester to a dictionary so I can look up a specific one to work with, but I am having trouble when I want to loop over all of them to do something like when I first set up a new semester I want to add all the sections, then loop over them and add students to each. If I try the same code to loop over the dictionary it gives me the key, but I was hoping to get the value.

I have also tried to iterate over a dictionary like this, which I got out of an older stack over flow question

for sec in iter(sorted(working_semester.sections.iteritems())):
    sec.addRosterFromFile(filename)

But iter(sorted ... returns a tuple (key, value) not the item so the line in side the loop gives me an error that tuple does not have a function called addStudent.

Currently I have this fix in place where I loop through the keys and then use the key to access the value like this: 

for key in working_semester.sections:
    working_semester.sections[key].addRosterFromFile(filename)

There has to be a way to loop over dictionary values, or is this not desirable? My understanding of dictionaries is that they are like lists but rather than grabbing an element by its position it has a specific key, which makes it easier to grab the one you want no matter what order they are in. Am I missing how dictionaries should be used?

Upvotes: 0

Views: 112

Answers (1)

BrenBarn
BrenBarn

Reputation: 251373

Using iteritems is a good approach, you just need to unpack the key and value:

for key, value in iter(sorted(working_semester.sections.iteritems())):
    value.addRosterFromFile(filename)

If you really only need the value, you could use the aptly named itervalues:

for sec in sorted(working_semester.sections.itervalues()):
    sec.addRosterFromFile(filename)

(It's not clear from your example whether you really need sorted there. If you don't need to iterate over the sections in sorted order just leave sorted out.)

Upvotes: 2

Related Questions