Constraints

pytypeinput uses Pydantic's Field to add validation constraints to parameters.

String Constraints

Min/Max Length

Limit string length:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class UserForm:
    username: Annotated[str, Field(min_length=3, max_length=20)]
    bio: Annotated[str, Field(max_length=500)]

params = analyze_dataclass(UserForm)

print(params[0].constraints)  # Field(min_length=3, max_length=20)
print(params[1].constraints)  # Field(max_length=500)

HTML Renderer Demo:

Try typing less than 3 or more than 20 characters!

Pattern (Regex)

Validate with regular expressions:

from dataclasses import dataclass
from pytypeinput import Field, PatternMessage, Annotated, analyze_dataclass

@dataclass
class AccountForm:
    username: Annotated[
        str,
        Field(pattern=r'^[a-zA-Z0-9_]+$'),
        PatternMessage("Only letters, numbers, and underscores allowed")
    ]

params = analyze_dataclass(AccountForm)

print(params[0].constraints)           # Field(pattern=...)
print(params[0].ui.pattern_message)    # "Only letters, numbers..."

HTML Renderer Demo:

Try entering special characters like @ or #!

Integer Constraints

Range (ge/le)

Constrain integer values with greater-or-equal (ge) and less-or-equal (le):

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class UserForm:
    age: Annotated[int, Field(ge=18, le=120)]
    rating: Annotated[int, Field(ge=1, le=5)]

params = analyze_dataclass(UserForm)

print(params[0].constraints)  # Field(ge=18, le=120)
print(params[1].constraints)  # Field(ge=1, le=5)

HTML Renderer Demo:

Try entering values outside the allowed range!

Strict Bounds (gt/lt)

Use greater-than (gt) and less-than (lt) for exclusive bounds:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class ScoreForm:
    percentage: Annotated[int, Field(gt=0, lt=100)]  # 1-99

params = analyze_dataclass(ScoreForm)

print(params[0].constraints)  # Field(gt=0, lt=100)

HTML Renderer Demo:

Values 0 and 100 are not allowed!

Float Constraints

Range (ge/le)

Constrain decimal values:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class ProductForm:
    price: Annotated[float, Field(ge=0.0, le=9999.99)]
    rating: Annotated[float, Field(ge=0.0, le=5.0)]

params = analyze_dataclass(ProductForm)

print(params[0].constraints)  # Field(ge=0.0, le=9999.99)
print(params[1].constraints)  # Field(ge=0.0, le=5.0)

HTML Renderer Demo:

Strict Bounds (gt/lt)

Exclusive bounds for floats:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class MeasurementForm:
    temperature: Annotated[float, Field(gt=-273.15)]  # Above absolute zero

params = analyze_dataclass(MeasurementForm)

print(params[0].constraints)  # Field(gt=-273.15)

HTML Renderer Demo:

List Constraints

List Length

Limit the number of items in a list:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class TagsForm:
    tags: Annotated[list[str], Field(min_length=1, max_length=5)]
    categories: Annotated[list[str], Field(min_length=2)]

params = analyze_dataclass(TagsForm)

print(params[0].list.constraints)  # Field(min_length=1, max_length=5)
print(params[1].list.constraints)  # Field(min_length=2)

HTML Renderer Demo:

Try adding/removing items - the + and × buttons are disabled when limits are reached!

Item Constraints

Apply constraints to individual list items:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class ScoresForm:
    scores: list[Annotated[int, Field(ge=0, le=100)]]
    names: list[Annotated[str, Field(min_length=2, max_length=50)]]

params = analyze_dataclass(ScoresForm)

print(params[0].constraints)  # Field(ge=0, le=100) - for each item
print(params[1].constraints)  # Field(min_length=2, max_length=50) - for each item

HTML Renderer Demo:

Each item is validated individually!

Combined List Constraints

Constrain both list length and item values:

from dataclasses import dataclass
from pytypeinput import Field, Annotated, analyze_dataclass

@dataclass
class TestForm:
    answers: Annotated[
        list[Annotated[int, Field(ge=1, le=5)]],
        Field(min_length=5, max_length=10)
    ]

params = analyze_dataclass(TestForm)

print(params[0].list.constraints)  # Field(min_length=5, max_length=10)
print(params[0].constraints)       # Field(ge=1, le=5)

HTML Renderer Demo:

Must have 5-10 items, each between 1-5!

Combined Constraints

Multiple constraints on a single field:

from dataclasses import dataclass
from pytypeinput import Field, PatternMessage, Annotated, analyze_dataclass

@dataclass
class RegistrationForm:
    username: Annotated[
        str,
        Field(
            min_length=3,
            max_length=20,
            pattern=r'^[a-zA-Z0-9_]+$'
        ),
        PatternMessage("Only letters, numbers, and underscores")
    ]
    age: Annotated[int, Field(ge=13, le=120)]

params = analyze_dataclass(RegistrationForm)

HTML Renderer Demo: