How can I store an instance of a class in a string? I tried eval, but that didn't work and threw SyntaxError. I would like this to work for user-defined classes and built-in classes (int, str, float).
Code:
class TestClass:
def __init__(self, number):
self.number = number
i = TestClass(14)
str_i = str(i)
print(eval(str_i)) # SyntaxError
print(eval("jkiji")) # Not Defined
print(eval("14")) # Works!
print(eval("14.11")) # Works!
The convention is to return a string with which you could instantiate the same object, if at all reasonable, in the __repr__ method.
class TestClass:
def __init__(self, number):
self.number = number
def __repr__(self):
return f'{self.__class__.__name__}({self.number})'
Demo:
>>> t = TestClass(14)
>>> t
TestClass(14)
>>> str(t)
'TestClass(14)'
>>> eval(str(t))
TestClass(14)
(Of course, you should not actually use eval to reinstantiate objects in this way.)
You can also use the pickle built-in module to convert an object to a byte string and back:
import pickle
class TestClass:
def __init__(self, number):
self.number = number
t1 = TestClass(14)
s1 = pickle.dumps(t1)
t2 = pickle.loads(s1)
then
print(t2.number)
will print
14
pickle.