How to Assign the Value of a Variable Using Eval in Python

How can I assign the value of a variable using eval in python?

Because x=1 is a statement, not an expression. Use exec to run statements.

>>> exec('x=1')
>>> x
1

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By the way, there are many ways to avoid using exec/eval if all you need is a dynamic name to assign, e.g. you could use a dictionary, the setattr function, or the locals() dictionary:

>>> locals()['y'] = 1
>>> y
1

Update: Although the code above works in the REPL, it won't work inside a function. See Modifying locals in Python for some alternatives if exec is out of question.

assign value to a variable using eval in a metaprogramming manner

Use exec instead:

sample = None
var_name = "sample"
value = 0
exec("{0} = {1}".format(var_name, value))

eval is for evaluating an expression, not an assignment statement

Python - How can I assign a value to eval

counterc = 0
countern = 0
counterx = 0
letter = input()

if letter in ['c','n','x']:
    globals()['counter{}'.format(letter)] += 1
    print(globals()['counter{}'.format(letter)])

Thank me later
if you are using python2 input 'c' of you are on py3 just type c without quotes.

Python Newbie: using eval() to assign a value to a self.variable

eval is a builtin not a default method for Python classes. But what you seek is setattr:

def replaceByTwo(self, var_name):
     setattr(self, var_name, 2)

Trial:

>>> t = trash()
>>> print(t.var2)
1
>>> t.replaceByTwo('var2')
>>> print(t.var2)
2

How to assign value to the output of eval function in python

Why don't you access your variables through globals() (or locals()) instead of eval?

d={'a':10}
globals()['d']['a']=15
print d['a']

in your particular case

d={'a':10}
s1='d'
s2='a'
globals()[s1][s2]=15
print d['a']

Mass producing variables using eval - python

You could use exec.

for i in range(100):
    exec('number_{0} = {0}'.format(i))

Python: Assign and Eval string to number

You can give to eval a dictionary to use as global variables:

print(eval(formula, dict1))

Using Eval in Python to create class variables

You can use the setattr function, which takes three arguments: the object, the name of the attribute, and it's value. For example,

setattr(self, 'wavelength', wavelength_val)

is equivalent to:

self.wavelength = wavelength_val

So you could do something like this:

for variable in self.variable_list:
       var_type,var_text_ctrl,var_name = variable
       if var_type == 'f' :
           setattr(self, var_name, var_text_ctrl.GetValue())

eval() does not assign variable at runtime

Use exec for statements:

>>> exec 'lis = [1,2,3]'
>>> lis
[1, 2, 3]

eval works only on expressions, like 2*2,4+5 etc

eval and exec are okay if the string is coming from a known source, but don't use them if the string is coming from an unknown source(user input).

Read : Be careful with exec and eval in Python

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