substring variable name python

Question

i have few variables like this:

self.lamp_1
self.lamp_2
self.lamp_3
self.lamp_4

and now i want to use each of this names is loop to call them automaticly, like this:

for i in range(1,5):
    self.canvas.itemconfig(self.lamp_/number_i_automaticly/, fill=self.color_blink)

I tried using function eval() but it doesn't work. It stops running my program.

eval("self.canvas.itemconfig(self.lamp_"+str(i)+",fill=self.color_blink)")

how can i declerate names of variables in that way, using key i?

Sven Marnach · Accepted Answer · 2012-02-09 11:04:04Z

8

Use a list instead of indexed variable names:

self.lamps = [lamp_1, lamp_2, lamp_3, lamp_4]

If you insist on using indexed variable names (you shouldn't), you can use getattr():

for i in range(1, 5):
    self.canvas.itemconfig(getattr(self, "lamp_%i" % i), 
                           fill=self.color_blink)

answered Feb 9, 2012 at 11:04

Sven Marnach

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5 Comments

anonf34 Over a year ago

getattr() doesn't work properly. it's says that's something wrong with arguments. what could that be?

Sven Marnach Over a year ago

@greg: How am I supposed to know? You neither told me what you tried nor what error message you got. :)

anonf34 Over a year ago

i find out what the problem was. this is for version 2.7 and I'm using 3.2, it works fine. thanks and sorry for weak comment.

Sven Marnach Over a year ago

@greg: There's no difference in the usage of getattr() between 2.7 and 3.2. The above code should work in both versions.

anonf34 Over a year ago

i don't know what was the problem than, i copy your version and there was and error. important is that we solved the problem ;)

Rob Wouters · Accepted Answer · 2012-02-09 11:06:50Z

2

You can use getattr for this:

for i in range(1,5):
    self.canvas.itemconfig(getattr(self, 'lamp_%s' % i),
                           fill=self.color_blink)

But you really shouldn't name your variables like this. Put them in a list and iterate over that:

self.lamps = [self.lamp_1, self.lamp_2, self.lamp_3, self.lamp_4]
for lamp in self.lamps:
    self.canvas.itemconfig(lamp, fill=self.color_blink)

answered Feb 9, 2012 at 11:06

Rob Wouters

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2 Comments

anonf34 Over a year ago

i used this: self.canvas.itemconfig(eval("self.lamp_{0}".format(i)), fill=self.color_blink) and it works fine! thanks a lot!!

Sven Marnach Over a year ago

@greg: It's a very bad idea to use indexed variable names. It's an even worse idea to use eval() instead of getattr() to access them. Do yourself a favour by not ignoring our advice! :)

Ricardo Cárdenes · Accepted Answer · 2012-02-09 11:16:58Z

2

Try to avoid using eval whenever possible. In this case you could use getattr:

for i in range(1, 5):
    value = getattr(self, 'lamp_%d' % i)

But I agree: you should be using a list (or a dictionary) instead.

Edit: oh, and use setattr to set them:

setattr(self, 'lamp_%d' % i, value)

answered Feb 9, 2012 at 11:16

Ricardo Cárdenes

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Comments

Kimvais · Accepted Answer · 2012-02-09 11:16:36Z

1

I suggest doing this as @SvenMarnach suggests. However, if you must use for some external reason lamp_1 etc, you should change your loop from range() to:

for lamp in (self.lamp_1, self.lamp_2, self.lamp_3, self.lamp_4):
    self.canvas.itemconfig(lamp, fill=self.color_blink)

answered Feb 9, 2012 at 11:16

Kimvais

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