[Tut] Python getattr()

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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

or

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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