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String Types


Strings are accepted as-is, bytes and bytearray are converted using v.decode(), enums inheriting from str are converted using v.value, and all other types cause an error


EmailStr requires email-validator to be installed. The input string must be a valid email address, and the output is a simple string


NameEmail requires email-validator to be installed. The input string must be either a valid email address or in the format Fred Bloggs <[email protected]>, and the output is a NameEmail object which has two properties: name and email. For Fred Bloggs <[email protected]> the name would be "Fred Bloggs". For [email protected] it would be "fred.bloggs".


ImportString expects a string and loads the Python object importable at that dotted path. Attributes of modules may be separated from the module by : or ., e.g. if 'math:cos' was provided, the resulting field value would be the functioncos. If a . is used and both an attribute and submodule are present at the same path, the module will be preferred.

On model instantiation, pointers will be evaluated and imported. There is some nuance to this behavior, demonstrated in the examples below.

A known limitation: setting a default value to a string won't result in validation (thus evaluation). This is actively being worked on.

Good behavior:

from math import cos

from pydantic import BaseModel, ImportString, ValidationError

class ImportThings(BaseModel):
    obj: ImportString

# A string value will cause an automatic import
my_cos = ImportThings(obj='math.cos')

# You can use the imported function as you would expect
cos_of_0 = my_cos.obj(0)
assert cos_of_0 == 1

# A string whose value cannot be imported will raise an error
except ValidationError as e:
    1 validation error for ImportThings
      Invalid python path: No module named '' [type=import_error, input_value='', input_type=str]

# Actual python objects can be assigned as well
my_cos = ImportThings(obj=cos)
my_cos_2 = ImportThings(obj='math.cos')
assert my_cos == my_cos_2

Serializing an ImportString type to json is also possible.

from pydantic import BaseModel, ImportString

class ImportThings(BaseModel):
    obj: ImportString

# Create an instance
m = ImportThings(obj='math:cos')
#> obj=<built-in function cos>
#> {"obj":"math.cos"}

Constrained Types

The value of numerous common types can be restricted using con* type functions.

Arguments to constr

The following arguments are available when using the constr type function

  • strip_whitespace: bool = False: removes leading and trailing whitespace
  • to_upper: bool = False: turns all characters to uppercase
  • to_lower: bool = False: turns all characters to lowercase
  • strict: bool = False: controls type coercion
  • min_length: int = None: minimum length of the string
  • max_length: int = None: maximum length of the string
  • pattern: str = None: regex to validate the string against