auto() Function

The auto() function automatically assigns values to enum members, eliminating tedious manual assignment.

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Basic auto() Usage

from enum import Enum, auto

class Color(Enum):
    RED = auto()
    GREEN = auto()
    BLUE = auto()

print(Color.RED)        # Color.RED
print(Color.RED.value)  # 1
print(Color.GREEN.value)  # 2
print(Color.BLUE.value)   # 3

# Values are auto-incremented starting from 1
for color in Color:
    print(f"{color.name} = {color.value}")

auto() with Flag

from enum import Flag, auto

class Permission(Flag):
    READ = auto()      # 1
    WRITE = auto()     # 2
    EXECUTE = auto()   # 4

# Flag auto() uses powers of 2
for perm in Permission:
    print(f"{perm.name} = {perm.value}")

# Allows bitwise operations
user_perms = Permission.READ | Permission.WRITE
print(user_perms)  # Permission.READ|WRITE

Customizing auto() Behavior

from enum import Enum, auto

class Priority(Enum):
    def _generate_next_value_(name, start, count, last_values):
        # Custom logic for auto values
        # name: member name
        # start: starting value
        # count: number of members so far
        # last_values: list of previous values
        return name.lower()

    LOW = auto()
    MEDIUM = auto()
    HIGH = auto()
    CRITICAL = auto()

print(Priority.LOW.value)        # 'low'
print(Priority.CRITICAL.value)   # 'critical'

auto() with Strings

from enum import Enum, auto

class HttpMethod(Enum):
    def _generate_next_value_(name, start, count, last_values):
        return name.upper()

    GET = auto()
    POST = auto()
    PUT = auto()
    DELETE = auto()
    PATCH = auto()

print(HttpMethod.GET.value)     # 'GET'
print(HttpMethod.DELETE.value)  # 'DELETE'

Mixing auto() and Manual Values

from enum import Enum, auto

class Status(Enum):
    PENDING = auto()      # 1
    APPROVED = auto()     # 2
    CUSTOM = "special"    # manual value
    REJECTED = auto()     # 3
    ARCHIVED = auto()     # 4

for status in Status:
    print(f"{status.name}: {status.value}")

auto() with IntEnum

from enum import IntEnum, auto

class HttpStatus(IntEnum):
    # Custom auto for specific patterns
    def _generate_next_value_(name, start, count, last_values):
        if count == 0:
            return 100
        elif count < 3:
            return 100 + (count - 1) * 10 + 1
        elif count < 6:
            return 200 + (count - 3) * 100
        else:
            return 400 + (count - 6) * 50

    CONTINUE = auto()          # 100
    SWITCHING = auto()         # 101
    PROCESSING = auto()        # 102
    OK = auto()                # 200
    CREATED = auto()           # 300
    BAD_REQUEST = auto()       # 400

print(HttpStatus.CONTINUE.value)     # 100
print(HttpStatus.OK.value)           # 200
print(HttpStatus.BAD_REQUEST.value)  # 400

auto() for String Slugs

from enum import Enum, auto

class ContentType(Enum):
    def _generate_next_value_(name, start, count, last_values):
        return name.lower().replace('_', '-')

    PLAIN_TEXT = auto()
    RICH_TEXT = auto()
    HTML_PAGE = auto()
    JSON_DATA = auto()

print(ContentType.PLAIN_TEXT.value)   # 'plain-text'
print(ContentType.HTML_PAGE.value)    # 'html-page'
print(ContentType.JSON_DATA.value)    # 'json-data'

When to Use auto()

• Ordering matters but exact value doesn't
• Avoiding manual typos in value assignment
• Natural progression (1, 2, 3, ...)
• Combined with custom _generate_next_value_ for domain-specific values