[Tut] Python getattr() - Printable Version

[Tut] Python getattr() - Printable Version

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[Tut] Python getattr() - xSicKxBot - 12-28-2020

Python getattr()

Python’s built-in

Code:
getattr(object, string)

function returns the value of the

Code:
object

‘s attribute with name

Code:
string

. If this doesn’t exist, it returns the value provided as an optional third

Code:
default

argument. If that doesn’t exist either, it raises an

Code:
AttributeError

. An example is

Code:
getattr(porsche, 'speed')

which is equivalent to

Code:
porsche.speed

Usage

Learn by example! Here’s an example on how to use the

Code:
getattr()

built-in function.

Code:
# Define class with one attribute
class Car: def __init__(self, brand, speed): self.brand = brand self.speed = speed # Create object
porsche = Car('porsche', 100)
tesla = Car('tesla', 110) # Two alternatives to get instance attributes:
print(getattr(porsche, 'brand') + " " + str(getattr(porsche, 'speed')))
print(tesla.brand + " " + str(tesla.speed)) # Get an attribute that doesn't exist with default argument:
print(getattr(porsche, 'color', 'red'))

The output of this code snippet is:

Code:
porsche 100
tesla 110
red

Syntax getattr()

The

Code:
getattr()

object has the following syntax:

Code:
Syntax:
getattr(object, attribute[, default]) # Get object's attribute value or default if non-existent

Arguments |

Code:
object

|
The object from which the attribute value should be drawn.

|

Code:
attribute

|
The attribute name as a string.

|

Code:
default

|
The return value in case the attribute doesn’t exist.

Return Value |

Code:
object

|
Returns the value of the

Code:
attribute

of instance

Code:
object

Code:
default

if non-existent.

Video getattr()

Return value from getattr()

The

Code:
getattr(object, attribute, default)

method returns one of the following:

the value of the
Code:
object
‘s
Code:
attribute
Code:
default
, if the attribute doesn’t exist
Code:
AttributeError
if neither the attribute exists, nor
Code:
default
is provided.

Interactive Shell Exercise: Understanding getattr()

Consider the following interactive code:

https://trinket.io/embed/python/48f2b083eb

Exercise: Fix the error in the code!

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Why Using getattr() Instead of Dot to Get an Attribute?

You’ve seen two alternatives to get an attribute:

Code:
getattr(object, attribute_str)
Code:
object.attribute

Why using the getattr() function over the more concise dot syntax?

There are two main reasons:

Code:
getattr()
provides a default value in case the attribute doesn’t exist whereas the dot syntax throws an error.
Code:
getattr()
allows to dynamically access the attribute with the string instead of the name. For example, you may obtain the string as a user input, in which case, you cannot use the dot syntax
Code:
object.attribute
because
Code:
attribute
is a string, not a name.

Related Functions

The
Code:
setattr()
function returns the value of an attribute.
The
Code:
hasattr()
function checks if an attribute exists.
The
Code:
delattr()
function deletes an existing attribute.

Summary

Python’s built-in

Code:
getattr(object, string)

function returns the value of the

Code:
object

‘s attribute with name

Code:
string

Code:
# Define class with one attribute
class Car: def __init__(self, brand, speed): self.brand = brand self.speed = speed porsche = Car('porsche', 100)
print(getattr(porsche, 'brand') + " " + str(getattr(porsche, 'speed')))
# porsche 100

If this doesn’t exist, it returns the value provided as an optional third

Code:
default

argument.

Code:
print(getattr(porsche, 'color', 'red'))
# red

If that doesn’t exist either, it raises an

Code:
AttributeError

Code:
print(getattr(porsche, 'color')) '''
Traceback (most recent call last): File "C:\Users\xcent\Desktop\Finxter\Blog\HowToConvertBooleanToStringPython\code.py", line 12, in <module> print(getattr(porsche, 'color'))
AttributeError: 'Car' object has no attribute 'color' '''

An example is

Code:
getattr(porsche, 'speed')

which is equivalent to

Code:
porsche.speed

Code:
print(getattr(porsche, 'speed'))
print(porsche.speed)
# Both print attribute value: 100

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