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Adwaith Rajesh
Adwaith Rajesh

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Storing python objects inside PysonDB

Let's see how we can store python objects, this include strings, list, function, etc.., inside a DB like pysonDB

Consider I've function foo which takes an argument x and return x * (x + x). Which I want to store inside a DB.

def foo(x: float) -> float:
    return x * (x + x)
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First things first we nee to convert this object to byte string. To do that we can use the pickle. module.

import pickle
byte_string = pickle.dumps(foo)
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This byte string cannot be directly added to a PysonDB database, as byte strings are not JSON serializable. So a simple workaround will be to add quotes around the byte string which can be easily done like this.

obj_string = f"{byte_string}"
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This string can be now added to the DB

from pysondb import db

a = db.getDb("test.json")
a.add({
    "name": "foo_function",
    "obj": obj_string
})
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To get the object back we can do the following steps.

data = a.getBy({"name": "foo_function"})
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Now data will look something like this.

[{'name': 'foo_function', 'obj': "b'\\x80\\x04\\x95\\x14\\x00\\x00\\x00\\x00\\x00\\x00\\x00\\x8c\\x08__main__\\x94\\x8c\\x03foo\\x94\\x93\\x94.'", 'id': 316182400052721056}]
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To convert the obj string back to a callable function. We can do the following.

str_obj = data[0]["obj"]
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Remember that str_obj is still a string and not a byte string, which is what we need, since the required byte string is inside this string, we can simply evaluate the string.

import ast
byte_obj = ast.literal_eval(str_obj) 
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To call the function we can do this.

call_obj = pickle.loads(byte_obj)
print(call_obj(3))

# output
18
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Entire Code

import ast
import pickle

from pysondb import db

def foo(x: float) -> float:
    return x * (x + x)

byte_string = pickle.dumps(foo)
obj_string = f"{byte_string}"

a = db.getDb("test2.json")
a.add({
    "name": "foo_function",
    "obj": obj_string
})

data = a.getBy({"name": "foo_function"})

str_obj = data[0]["obj"]
byte_obj = ast.literal_eval(str_obj)

call_obj = pickle.loads(byte_obj)
print(call_obj(3))

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So we have successfully stored a python object inside a DB. The steps are the same for all the objects like list or dict.

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