How can I create an array/list of dictionaries in python?

Question

I have a dictionary as follows:

{'A':0,'C':0,'G':0,'T':0}

I want to create an array with many dictionaries in it, as follows:

[{'A':0,'C':0,'G':0,'T':0},{'A':0,'C':0,'G':0,'T':0},{'A':0,'C':0,'G':0,'T':0},{'A':0,'C':0,'G':0,'T':0},...]

This is my code:

weightMatrix = []
for k in range(motifWidth):
    weightMatrix[k] = {'A':0,'C':0,'G':0,'T':0}

But of course it isn't working. Can someone give me a hint? Thanks.

Answer 1

Use

weightMatrix = []
for k in range(motifWidth):
    weightMatrix.append({'A':0,'C':0,'G':0,'T':0})

Answer 2

I assume that motifWidth contains an integer.

In Python, lists do not change size unless you tell them to. Hence, Python throws an exception when you try to change an element that isn't there. I believe you want:

weightMatrix = []
for k in range(motifWidth):
    weightMatrix.append({'A':0,'C':0,'G':0,'T':0})

For what it's worth, when asking questions in the future, it would help if you included the stack trace showing the error that you're getting rather than just saying "it isn't working". That would help us directly figure out the cause of the problem, rather than trying to puzzle it out from your code.

Hope that helps!

Answer 3

weightMatrix = [{'A':0,'C':0,'G':0,'T':0} for k in range(motifWidth)]

Answer 4

I'm going to assume you want a quick one-liner for this. dan04 has a good solution. You might also want to check this out:

weightMatrix = [{'A':0,'C':0,'G':0,'T':0}] * motifWidth