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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Use Color("red") when the string is an enum member’s value, and Color["RED"] when it is the member’s name. The two lookups can accept different strings and raise different exceptions when no match exists.
Choose lookup by value or by name
For a string-valued enum, calling the enum class looks up a member by its value. Square-bracket access looks up a member by its name, as shown in the Python Enum HOWTO and PEP 435.
from enum import Enum
class Color(Enum):
RED = "red"
GREEN = "green"
by_value = Color("red") # Color.RED
by_name = Color["RED"] # Color.RED
Both expressions return an enum member, not a plain string. Read its declared name with .name and its associated value with .value:
by_value.name # "RED"
by_value.value # "red"
| What the input string represents | Lookup | Exception if no match exists |
|---|---|---|
Member value, such as "red" |
Color("red") |
ValueError |
Member name, such as "RED" |
Color["RED"] |
KeyError |
The Python 3.12 enum reference documents the attributes and lookup behavior.
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Handle input that does not match
Catch the exception for the lookup you chose at the point where untrusted or optional input enters the application. For example, return a fallback when a value lookup fails:
try:
color = Color(raw_value)
except ValueError:
color = None
For name lookup, catch KeyError instead. If invalid input should be rejected, let the lookup exception propagate or translate it into a clearer application-level error. Avoid catching broad Exception, which can conceal unrelated defects.
Make case and whitespace rules explicit
Name lookup uses the supplied name; do not assume it ignores case or surrounding whitespace. If the input contract allows case-insensitive matching and trimming, normalize before indexing:
color = Color[raw_name.strip().upper()]
This works only when enum names follow the same uppercase convention. Trimming and case-folding are application policies, not built-in case-insensitive enum lookup.
When to use StrEnum
A regular Enum with string values already supports conversion with Color("red"). Choose StrEnum when members should also behave as strings in many contexts, rather than just to enable lookup. StrEnum was added in Python 3.11, so projects supporting earlier Python versions cannot rely on it.
The enum reference describes StrEnum as having members that are also strings and can be used in most of the same places as strings. Some standard-library locations check for an exact str type; use str(member) there if needed. String operations on a StrEnum member produce ordinary strings, not enum members. See the enum reference and Enum HOWTO.
Understand duplicate values and aliases
By default, two enum names may share a value. The later name is an alias: looking up the shared value returns the canonical member, normal iteration omits aliases, and the read-only __members__ mapping includes every name. If duplicate values should make the enum definition invalid, apply @unique:
from enum import Enum, unique
@unique
class Color(Enum):
RED = "red"
GREEN = "green"
Alias behavior and uniqueness are described in the Enum HOWTO, enum reference, and PEP 435.
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