CODEWITHSUNDEEP
pythonvariablesdynamic
DaneSoul
DaneSoul

Reputation: 4511

Access to value of variable with dynamic name

I found several topics where discussed that dynamical creating of single variables in loops is bad practice and better use dictionary.

In my case I don't need create them dynamically, I want access them in the loop.

I don't want to use dictionary for them, because these variables are used in lot of places in code, and only in one place I need such dynamic access.

Idea example:

car_pos = 1; man_pos = 10
car_vel = 100; man_vel = 5

for elm in ['car', 'man']:
    elm_pos = elm + '_pos'
    elm_vel = elm + '_vel'
    # I want values of elements with such names here
    print(elm_pos, elm_vel)

# Desired output:
# (1, 100)
# (10, 5)

Upvotes: 3

Views: 1377

Answers (3)

kindall
kindall

Reputation: 184171

Variable names are a terrible way to relate pieces of information. There is nothing linking man_pos and man_vel except that they both happen to start with man. Other than that they are totally separate. Python has better ways of bundling elements like these together.

In this case, man and car should be objects with attributes pos and vel. 

class Thing:
    def __init__(self, pos, vel):
        self.pos = pos
        self.vel = vel

# assume that both men and cars move only in one dimension
man = Thing(10, 2)   
car = Thing(100, -5)

Then your loop is simply:

for item in [car, man]:
    print(item.pos, item.vel)

Do not do it the way you're trying to do it. It will only lead to tears -- if not yours, then of the people who have to look at your code.

Upvotes: 4

Sarith Subramaniam
Sarith Subramaniam

Reputation: 246

Agree with everything that kindall said. However, you can try named tuple to go the non dictionary route... 

from collections import namedtuple
data = namedtuple('data',('pos','vel'))
car = data(1,100)
man = data(10,5)


for elm in (car,man):
    print(elm.pos,elm.vel)

Upvotes: 1

Saksham Varma
Saksham Varma

Reputation: 2130

Just use the globals() dictionary, with key as your variable names. The value for these keys would be the actual value of these variables. 

car_pos = 1; man_pos = 10
car_vel = 100; man_vel = 5

for elm in ['car', 'man']:
    elm_pos = elm + '_pos'
    elm_vel = elm + '_vel'

    print(globals()[elm_pos], globals()[elm_vel])

Upvotes: 2

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