Strings in Python are commonly used to represent values like status codes, settings, or user selections. However, when working with structured data or making comparisons, using Enums provides better organization and error handling.
For example, you might receive user input as a string like “COMPLETED” but want to treat it as an Enum value in your program.
In such situations, it becomes essential to convert a string to an Enum. This allows you to take advantage of Enum features.
Enums in Python
Before getting into string conversion, let’s quickly understand Enums. Added in Python 3.4, the enum module provides a way to create sets of symbolic names bound to unique values. They’re particularly useful for defining constants and categorical values.
from enum import Enum
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3Enums provide type safety, better readability, and help catch errors during development rather than at runtime.
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Convert String to Enum in Python
Let me explain to you the important methods to convert string to enum in Python.
Method 1: Use the getattr() Method
The most simple approach to convert a string to an Enum in Python is using the built-in getattr() function. This method is widely recognized as the standard solution.
from enum import Enum
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3
# Convert string to Enum
color_name = "RED"
color_enum = getattr(Color, color_name)
print(color_enum)
print(color_enum.value)Output:
Color.RED
1I executed the above example code and added the screenshot below.
Handle Invalid Strings
One issue with getattr() is that it raises an AttributeError if the Python string doesn’t match any Enum member. Here’s how to handle this gracefully:
try:
color_enum = getattr(Color, color_name)
except AttributeError:
print(f"'{color_name}' is not a valid Color")
# Optional: set a default value
color_enum = Color.REDCheck out How to Concatenate String and Int in Python?
Method 2: Use Enum(value) for Reverse Lookup
Sometimes you might have the value and want to get the Enum member in Python. This is a bit different from our main topic but useful to know:
from enum import Enum
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3
# Finding Enum member by value
value = 2
color_enum = Color(value)
print(color_enum)Output:
Color.GREENI executed the above example code and added the screenshot below.
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Method 3: Create a Custom Conversion Method
This approach is especially useful when working in large applications where robust error handling and user-friendly messages are important.
from enum import Enum
class Color(Enum):
RED = 1
GREEN = 2
BLUE = 3
class ColorConverter:
@staticmethod
def from_string(color_name, case_sensitive=True):
try:
if case_sensitive:
return getattr(Color, color_name)
else:
return getattr(Color, color_name.upper())
except AttributeError:
valid_colors = [c.name for c in Color]
raise ValueError(f"Invalid color '{color_name}'. Valid options are: {valid_colors}")
#usage
red = ColorConverter.from_string("RED")
print(f"Red color enum: {red}")
green = ColorConverter.from_string("green", case_sensitive=False)
print(f"Green color enum: {green}")Output:
Red color enum: Color.RED
Green color enum: Color.GREENI executed the above example code and added the screenshot below.
Using a custom conversion method allows you to gracefully manage input variations and errors when mapping strings to enums.
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Method 4: Use Enum Auto-Conversion
The Enum module in Python is quite powerful, and with a bit of customization, we can create an Enum subclass that handles string conversion automatically:
from enum import Enum
class StringEnum(str, Enum):
"""An Enum that can be created from a string."""
@classmethod
def from_string(cls, s):
try:
return cls[s]
except KeyError:
raise ValueError(f"{s} is not a valid {cls.__name__}")
class Fruit(StringEnum):
APPLE = "apple"
BANANA = "banana"
ORANGE = "orange"
# Usage
fruit = Fruit.from_string("APPLE")
print(fruit) # Output: Fruit.APPLERead How to Remove HTML Tags from a String in Python?
Method 5: Use a Dictionary Mapping
For scenarios where Enum names might not match the input strings exactly (like handling different formats or abbreviations), a dictionary mapping in Python can be useful:
from enum import Enum
class State(Enum):
CALIFORNIA = 1
NEW_YORK = 2
TEXAS = 3
FLORIDA = 4
# Mapping of possible string inputs to Enum members
state_mapping = {
"CA": State.CALIFORNIA,
"California": State.CALIFORNIA,
"calif": State.CALIFORNIA,
"NY": State.NEW_YORK,
"New York": State.NEW_YORK,
"TX": State.TEXAS,
"Texas": State.TEXAS,
"FL": State.FLORIDA,
"Florida": State.FLORIDA
}
def get_state_from_string(state_string):
normalized_string = state_string.strip()
return state_mapping.get(normalized_string, None)
# Usage
state = get_state_from_string("CA")
print(state) # Output: State.CALIFORNIAHandle Case Sensitivity in Python String to Enum Conversion
Case sensitivity is often a challenge when converting strings to Enums. Here are different approaches to handle this:
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Option 1: Case-Insensitive Lookup
This function takes an Enum class and a string name, loops through all the members of the enum, and compares each member’s name with the provided string in a lowercase format.
def get_enum_case_insensitive(enum_class, name):
for enum_member in enum_class:
if enum_member.name.lower() == name.lower():
return enum_member
return None
# Usage
color = get_enum_case_insensitive(Color, "red") # Returns Color.REDWe define a helper function called get_enum_case_insensitive() that allows us to perform case-insensitive lookups on Enum members.
Option 2: Create a Case-Insensitive Enum Class
The custom implementation checks if the input is a string and compares it to the names of enum members in a case-insensitive way.
class CaseInsensitiveEnum(Enum):
@classmethod
def _missing_(cls, value):
if isinstance(value, str):
for member in cls:
if member.name.lower() == value.lower():
return member
return None
class Weekday(CaseInsensitiveEnum):
MONDAY = 1
TUESDAY = 2
WEDNESDAY = 3
THURSDAY = 4
FRIDAY = 5
# Usage
day = Weekday("monday") # Returns Weekday.MONDAYWe create a custom base class named CaseInsensitiveEnum that inherits from Python’s built-in Enum.
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Extend Enum Functionality
Extending Python’s built-in Enum class allows us to add extra functionality that makes working with enums more convenient.
from enum import Enum, auto
class ExtendedEnum(Enum):
@classmethod
def list_names(cls):
return [c.name for c in cls]
@classmethod
def list_values(cls):
return [c.value for c in cls]
@classmethod
def from_string(cls, s):
try:
return getattr(cls, s)
except AttributeError:
return None
class Planet(ExtendedEnum):
MERCURY = auto()
VENUS = auto()
EARTH = auto()
MARS = auto()
# Usage
print(Planet.list_names()) # ['MERCURY', 'VENUS', 'EARTH', 'MARS']
earth = Planet.from_string("EARTH") # Planet.EARTHThis approach promotes cleaner, more maintainable code when working with enums across your application.
In this article, I explained how to convert string to enum in Python. I explained methods like using the getattr() method, using enum(value) for reverse lookup, creating a custom conversion method, enum auto-conversion, and using dictionary mapping. I also covered how to handle case sensitivity while converting and extending enum functionality.
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I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.
