How to update a list of variables in python?

you need to update the list and not the variable:

a = 1
b = 2
lst = [a, b]  # the list now stores the references a and b point to
              # changing a later on has no effect on this!  
lst[0] = 2

and please do not use list as variable name! this is a keyword built-in type in python and overwriting it is a very bad idea!

if you only know the value of the element in the list (and this value is unique) you could do this:

old_val = 2
new_val = 3

lst[lst.index(old_val)] = new_val

Why don't you use dictionary??

With dictionary:

_dict = {}
_dict["a"] = 1
_dict["b"] = 2
print _dict["a"] # prints 1

Now if you want to set and get value of variable "a":

_dict["a"] = 2
print _dict["a"] # prints 2

At the assignment 'a=1' an integer object is created with the value 1. That object is added to your list. At the second assignment (a=2) a new object is created, but the old one still is in the list, its value unchanged. That is what you see.

To change this behaviour, the value of the object must be changed. Ints are immutable in Python, meaning that exactly this, i.e. changing the value, is not possible. You'll have to define your own and then change its value. For example:

class MyInt(object):

    def __init__(self, value):
        self.setValue(value)

    def setValue(self, value):
        self.value = value

    def __repr__(self):
        return str(self.value)

a=MyInt(1)
print(dir(a))
b=2
list = [a,b] #user defined order
print (list) # 1,2
a.setValue(2)
print (list) # prints 2,2

It is not clean but a work around trick , you can assign the value of a is a single element list

a = [1]
b = 2

So when you assign them to a list:

lst = [a,b]

and change the value of a by calling its 0th element:

a[0] = 2

it will also change the referenced list that is a

print(lst)
#[[2],2]

likewise if you place the value in the list:

lst[0][0] = 2
print(a[0])
#2

You can define a function:\

a, b = 1, 2

def list_():
   return [a, b]

list_() # [1, 2]

a = 2
list_() # [2, 2]

What I've done to get around this is just make a function to update/redefine the list that I can call after updating variables. Kind of dirty but it works and is fast.

def updateList():
   lst = [a,b]

This will make the list refresh its contents with the newest variable values, allowing the following:

a=1
b=2
list = [a,b]
a=2
updateList()
print(lst)

Depending on how often you need to update the elements this may help.