Constructing variables within a for loop

Question

Let's say I want to create a lot of instances of a class but don't want to write the variable name down for every instance.

What I want:

value1 = class(value1)
value2 = class(value2)
.
.
.

My idea was:

list = ['One','Two','Three']

for value in list:
    value = class(value)

The result is not what I wanted. Python creates the variable 'value' and overrides it with the values of the list.

I'm sorry to ask such a basic question, but I'm not sure how to handle this.

Use a container like a list or a dict, in this case, a list seems appropriate — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Mar 21, 2019 at 18:09

Vasilis G. · Accepted Answer · 2019-03-21 18:17:18Z

1

First of all, note that you should not use list as a variable name, as it is reserved as a keyword by Python itself. Then, you could have another list, instanceList lets say, in which you will append every newly created instance of a class:

myList = ['One','Two','Three']
instanceList = []

for value in myList:
    instanceList.append(class(value))

answered Mar 21, 2019 at 18:17

Vasilis G.

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cglacet · Accepted Answer · 2019-03-21 18:17:04Z

1

You can use a list comprehension to build a list of class instances from a list of values:

class A:
    def __init__(self, value):
        self.value = value

values = ['One','Two','Three']
instances = [A(v) for v in values]

>>> print(list(o.value for o in instances))
['One', 'Two', 'Three']

answered Mar 21, 2019 at 18:17

cglacet

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2 Comments

Blorgbeard Over a year ago

[A(v) for v in values] is a list comprehension - he just uses a generator expression to print the results.

cglacet Over a year ago

I'm not sure to understand your question/remark, but if you need a generator instead of a list, then you can just replace instances = [...] by instances = (...). Another legitimate option is to use a for-loop as mentioned in this answer.

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