Let’s find out how we can put this function to use, using some simple examples.<\/p>\n\n\n\n
\nvalue = getattr(object, attribute_name[, default_value])\n<\/pre><\/div>\n\n\nHere, we pass object<\/code> to getattr()<\/code>. It tries to fetch attribute_name<\/code> (which must be a string) of this object. If the attribute exists, it will give us the corresponding value<\/code>.<\/p>\n\n\n\nThis is equivalent to the syntax:<\/p>\n\n\n
\nvalue = object.attribute_name\n<\/pre><\/div>\n\n\nOtherwise, there are two cases:<\/p>\n\n\n\n
- If the default value (
default_value<\/code>) is provided, it will simply use it and return the value of this default value.<\/li>- Otherwise, it will simply raise an
AttributeError<\/code> Exception, since our attribute is not found.<\/li><\/ul>\n\n\n\nThe point of getattr()<\/code> is to not only get the attribute value, but to also check that it exists!<\/p>\n\n\n\nLet’s now look at a few examples, to better our understanding.<\/p>\n\n\n\n
\n\n\n\nUsing getattr() – Some Examples<\/h2>\n\n\n\n
Let’s take a simple example first, where you have a Student class, with name<\/code> and roll_num<\/code> attributes. We’ll get them using getattr()<\/code>.<\/p>\n\n\n\nclass Student():\n def __init__(self, name, roll_no):\n self.name = name\n self.roll_no = roll_no\n\nstudent = Student('Amit', 8)\n\nprint(f"Name: {getattr(student, 'name')}")\nprint(f"Roll No: {getattr(student, 'roll_no')}")\n<\/pre><\/div>\n\n\nOutput<\/strong><\/p>\n\n\n\nName: Amit\nRoll No: 8\n<\/pre><\/div>\n\n\nIndeed, we did set the correct attributes, and we get them back using getattr()<\/code>!<\/p>\n\n\n\nNow, in this case, since both the attributes were there, no errors occurred. However, let’s try to get an attribute which we haven’t put inside the class; for example – age<\/code>.<\/p>\n\n\n\nclass Student():\n def __init__(self, name, roll_no):\n self.name = name\n self.roll_no = roll_no\n\nstudent = Student('Amit', 8)\n\nprint(f"Name: {getattr(student, 'name')}")\nprint(f"Roll No: {getattr(student, 'roll_no')}")\n\n# Will raise 'AttributeError' Exception since the attribute 'age' is not defined for our instance\nprint(f"Age: {getattr(student, 'age')}")\n<\/pre><\/div>\n\n\nOutput<\/strong><\/p>\n\n\n\nName: Amit\nRoll No: 8\nTraceback (most recent call last):\n File "getattr_example.py", line 12, in <module>\n print(f"Age: {getattr(student, 'age')}")\nAttributeError: 'Student' object has no attribute 'age'\n<\/pre><\/div>\n\n\nHere, we tried to retrieve an attribute which wasn’t defined. Since there were no default options, Python directly raised an Exception.<\/p>\n\n\n\n
If we want to set the default option to '100'<\/code>, then in this case, although we try to get age<\/code>, since it isn’t there, it will return 100 <\/code>instead.<\/p>\n\n\n\nLet’s test it out.<\/p>\n\n\n
\nclass Student():\n def __init__(self, name, roll_no):\n self.name = name\n self.roll_no = roll_no\n\nstudent = Student('Amit', 8)\n\nprint(f"Name: {getattr(student, 'name')}")\nprint(f"Roll No: {getattr(student, 'roll_no')}")\n\n# Will not raise AttributeError, since a default value is provided\nprint(f"Age: {getattr(student, 'age', 100)}")\n<\/pre><\/div>\n\n\nOutput<\/strong><\/p>\n\n\n\nName: Amit\nRoll No: 8\nAge: 100\n<\/pre><\/div>\n\n\n
\n\n\n\nWhy should you use getattr() ?<\/h2>\n\n\n\n
Since we mentioned earlier that this function is equivalent to object.attribute_name<\/code>, what is the point of this function?<\/p>\n\n\n\nWhile the above statement using dot notation is true, it is valid only when the attribute name is actually defined at the time of calling!<\/p>\n\n\n\n
So, if your classes are such that the object structure keeps changing from time to time, you could use getattr()<\/code> to check whether the object is in some particular state!<\/p>\n\n\n\nIt also gives us a very good way to easily handle exceptions and also provide fallback default values. In case something went wrong, we could either catch the AttributeError<\/code> exception or inspect the default value.<\/p>\n\n\n\nHope that makes it a bit more clearer as to why this may be useful for you!<\/p>\n\n\n\n
\n\n\n\nConclusion<\/h2>\n\n\n\n
We learned about how we could use the getattr()<\/code> function to retrieve the attributes of an object during runtime.<\/p>\n\n\n\n