Django Key (id)=(244584) already exists, Django unique constraint primary key

Razyesh Pudasaini — Wed, 18 Jan 2023 15:17:22 GMT

Replace stock_price with the table name on which you got the unique constraint issues.

SELECT MAX(id) FROM stock_price;

ALTER SEQUENCE stock_price_id_seq START WITH 245000;

ALTER SEQUENCE stock_price_id_seq RESTART;

Python walrus operator is weird...

Razyesh Pudasaini — Wed, 11 Aug 2021 15:50:06 GMT

Python walrus operator (:=) was introduced in Python 3.8. This operator helps most of the developers to assign variables in the middle of an expression.

Let's have a quick look, how walrus operator comes into hand.

def add(x):
      return x + 1

# before using walrus operator 
if add(x) > 5:
    return add(x)

# using walrus operator
if (res := add(x)) > 5:
    return res

Before using the walrus operator we are calling the add function twice, but using the walrus operator we don't have to call the walrus operator twice.

So, What is weird about walrus operator (actually its a fact)

1. Operator Precedence

def add(x):
      return x + 1

# using walrus operator
if res := add(x) > 5:
    return res

So, what do you think after removing the parenthesis, what it will be going to return (a number)?? Actually, it will return a Boolean (False or True) because of operator precedence. Since the Comparison operator has higher precedence it will be going to execute first and Boolean value will be assigned to res and it will return Boolean.

2. Direct Assignment

Walrus operators come into hand during the execution of valid expressions, Like if or for statements.

a := add(x) # gives error
(a := add(x)) # doesn't give error
print(a)