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

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 — Nitzle
– Nitzle, Commented Jun 15, 2015 at 17:28

deets · Accepted Answer · 2015-06-15 17:31:09Z

5

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.

answered Jun 15, 2015 at 17:31

deets

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Comments

jme · Accepted Answer · 2015-06-15 17:30:45Z

3

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

answered Jun 15, 2015 at 17:30

jme

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Comments

cfraschetti · Accepted Answer · 2015-06-15 17:32:17Z

-1

Not the most secure solution but you could use exec:

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

answered Jun 15, 2015 at 17:32

cfraschetti

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3 Comments

deets Over a year ago

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 Over a year ago

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 Over a year ago

@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

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