Naming a new list from another list in Python

Question

this may sound like a strange question from a Python noob, but here's the deal. I have a list with a bunch of (string) entries. I want to take one of those entries, add another string to the end of it, and then create a new array with that name. Eg, I have

list=["foo","bar"]

and I want to get something to the effect of

fooblah = []

I've been trying to do it this way

list[0] + "blah" = []

Obviously this doesn't work because the first part is a string instead of a variable name, but I'm not sure how to fix it. From what I've read of other people's problems, the solution might be in using a dictionary instead (?), but to be honest I'm not really sure how dictionaries work yet.

Thanks, J.

You can think of a dictionary as a type that maps one thing to another -- just like a real dictionary maps words to their definitions. You still access elements through the [ ] operator just like arrays, except that the keys don't have to be integers. — Cameron
– Cameron, Commented Mar 11, 2011 at 5:25

GWW · Accepted Answer · 2011-03-11 05:20:52Z

6

I would use a python dictionary they can use practically anything as an index instead of integers. You're code could get messy and unreadable really fast if you are dynamically creating local / global variables.

For example

l = ["foo","bar"]
d = {}
d[l[0] + "blah"] = []
d[l[0] + "blah"].append("foo")

Using a dictionary will give you some other neat advantages, for example, you can loop through all of the new lists you create.

for k,v in d.iteritems():
    print "{0} --> {1}".format(k,v)

answered Mar 11, 2011 at 5:20

GWW

44.3k11 gold badges119 silver badges110 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Cameron · Accepted Answer · 2011-03-11 05:19:46Z

1

Well, if you really want to do this one way would be through the globals() or locals() methods which return a dictionary of the current symbols:

globals()[list[0] + 'blah'] = [  ]

Note that list is the name of a built-in type, so using it as your variable name is considered bad practice.

Also, this is a highly unusual need; what exactly are you trying to accomplish? Perhaps there is a better way?

answered Mar 11, 2011 at 5:19

Cameron

99.4k29 gold badges206 silver badges233 bronze badges

3 Comments

JustinS Over a year ago

Yeah, sorry, it's not actually the variable name; I was just using it as an example (obviously not a very good one). Basically I have a list of all the directories in a folder, each one named for a different exposure. If the directory has a certain file in it, I want to read that whole file into a new array, but to keep each exposure separate it would be nice if that new array could somehow be named in a way that lets me know which exposure it came from. Is there a better way? I don't doubt it, but like I said I'm pretty new at this.

Cameron Over a year ago

@JustinS: Definitely a case for dictionaries (see GWW's answer). The exposure folder name could be the key, with the file contents as the value (if I interpreted correctly). Then you could do all sorts of nice things with the dictionary that you couldn't with variables, such as loop over them easily.

JustinS Over a year ago

Yup, that's what we're going to go with. Thanks for your and @GWW 's advice.

Collectives™ on Stack Overflow

Naming a new list from another list in Python

2 Answers 2

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related