calling string as variable in python

Question

I created a class called SignalParam in python containing different properties (frequency, voltage, time, etc)

I would like to create many instances of this type

vars()['Segment'+str(segment_number)] = SignalParam()

this line is working and i can create variables "Segment1", "Segment2", ....

My question is: i would like to call those variabes like

"Segment"+segment_number.freqency=33

• Nitzle: This seems better suited for a dictionary. Why not set the values with your key being a string constructed like you posted above? my_dict["Segment"+segment_number.frequency] = 33

Answer 1

This is bad style. Use a dictionary instead, and simple keys to access:

 d = {}
 d['Segment'+str(segment_number)] = SignalParam()
 d['Segment'+str(segment_number)].frequency = 33

The reason you shouldn't use vars is because it means you create global variables, which you should avoid. And given your access-style, you don't even need it.

Answer 2

It's probably better to use a dictionary here. Define one with segments = {}. Then you can create a SignalParam by keying into your dictionary with your segment number:

segments[segment_number] = SignalParam()

and use the object like this:

segments[segment_number].frequency = 33

Answer 3

Not the most secure solution but you could use exec:

exec("Segment"+segment_number+".frequency=33")

• deets: It is better to forget that exec exists. In my +15 years of python, I found maybe 2.3 legit uses deep in meta-programming. It's like giving a toddler a gatling gun. No idea what it does, but it's funny revolving...
• Alex Huszagh: deets, do you have any links the legitimate uses? I'm intrigued, as a former toddler who no longer sees any use for the gattling gun.
• deets: @AlexanderHuszagh this is one I can remember: re-creating the signature of a decorated function so you get proper error-messages on them github.com/micheles/decorator/blob/master/src/decorator.py