Pydantic: Error handling

Pydnatic throws ‘ValidationError’ whenever it see an issue while validating the data.

 

validation_error_1.py

from pydantic import BaseModel, ValidationError, conint, constr

class Employee(BaseModel):
    id: int
    name: constr(min_length=3, max_length=10)
    age: conint(gt=18)

try:
    emp1 = Employee(id = 1, name = 'Pt', age = 8)
except ValidationError as e:
    print(e)

 

Output

2 validation errors for Employee
name
  ensure this value has at least 3 characters (type=value_error.any_str.min_length; limit_value=3)
age
  ensure this value is greater than 18 (type=value_error.number.not_gt; limit_value=18)

As you see the output, Pydantic will return the list of errors found in the input data.

 

Different ways to extract the information from ValidaitonError object

Method	Description
e.errors()	method will return list of errors found in the input data.
e.json()	method will return a JSON representation of errors.
str(e)	method will return a human readable representation of the errors.

 

validation_error_2.py

from pydantic import BaseModel, ValidationError, conint, constr

class Employee(BaseModel):
    id: int
    name: constr(min_length=3, max_length=10)
    age: conint(gt=18)

try:
    emp1 = Employee(id = 1, name = 'Pt', age = 8)
except ValidationError as e:
    print(e.errors())
    print('\n\n\n')
    print(e.json())
    print('\n\n\n')
    print(str(e))

Output

[{'loc': ('name',), 'msg': 'ensure this value has at least 3 characters', 'type': 'value_error.any_str.min_length', 'ctx': {'limit_value': 3}}, {'loc': ('age',), 'msg': 'ensure this value is greater than 18', 'type': 'value_error.number.not_gt', 'ctx': {'limit_value': 18}}]




[
  {
    "loc": [
      "name"
    ],
    "msg": "ensure this value has at least 3 characters",
    "type": "value_error.any_str.min_length",
    "ctx": {
      "limit_value": 3
    }
  },
  {
    "loc": [
      "age"
    ],
    "msg": "ensure this value is greater than 18",
    "type": "value_error.number.not_gt",
    "ctx": {
      "limit_value": 18
    }
  }
]




2 validation errors for Employee
name
  ensure this value has at least 3 characters (type=value_error.any_str.min_length; limit_value=3)
age
  ensure this value is greater than 18 (type=value_error.number.not_gt; limit_value=18)

{

    "loc": [

      "age"

    ],

    "msg": "ensure this value is greater than 18",

    "type": "value_error.number.not_gt",

    "ctx": {

      "limit_value": 18

    }

  }

As you see above snippet, each error object contain properties loc, msg, type and ctx. Below table summarizes the properties.

 

Property	Description
loc	Specifies the error's location as a list. The first item in the list will be the field where the error occurred,
msg	Human readable error message
type	Computer readable identifier for the error type
ctx	an optional object which contains values required to render the error message.

 

  

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