How does Python language know about the type of identifiers?

How does Python language know about the type of identifiers?

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I recently faced this question..

How does python identifies the type of an identifier?

For example

a=5
b=6
c=a+b

the value of c is 11

Where as

x="hello"
y="world"
z=x+y

the value of z is "helloworld"

How does Python distinguishes these two cases?


In Python, types are not associated with variable names, but with values. The name 'a' does not hold any type information, it's the value '1' that holds that information (namely that it's an 'int' class).

This is a contract to C and Java, where types are associated with variable names.

This is exactly the difference between the Curry-style typing system and Church-style system.

http://en.wikipedia.org/wiki/Simply_typed_lambda_calculus#Intrinsic_vs._extrinsic_interpretations

C and Java use Church typing (variable name has a type) while Python and JavaScript use Curry typing (value has a type).

Python Keywords and Identifiers, You should know there are 33 keywords in Python programming language as of writing this tutorial. Although the number can vary in course of time. Also keywords  Elite Programming Professionals Ready to Teach Online. Anytime, Anywhere.


Check the __add__ method for classes.

What really happens is that the __add__ method of the object is called:

a + b is really a.__add__(b)

Check also diveintopython for special method names.

From the doc:

The int type implements the numbers.Integral abstract base class.

Likewise, strings are instances of the str class.

Python Keywords and Identifiers (Variable names), In this tutorial, you will learn about keywords (reserved words in Python) and An identifier is a name given to entities like class, functions, variables, etc. in Python. Statements & Comments · Python Variables · Python Datatypes · Python Type They are used to define the syntax and structure of the Python language. Looking for learn python programming? Search now! eTour.com is the newest place to search, delivering top results from across the web.


The python interpreter does not identify the types of identifier. Rather, it identifies the types of the objects referred to by the identifiers. The identifiers or names you declare does not hold the objects but rather refer to the objects and these objects, as pointed out by the previous answers, holds type information about themselves. These python objects are implemented as PyObject structure in C, which has a field PyObject *ob_type pointing to their types (being PyObject as well).

With the background above, now here is what happens when python runs your script.

  1. i = 1: it creates an object for the numeric 1 from the int type.
  2. A name i is bound to the int object created just now. By "bound to" I means inserting an entry into the global dictionary (you can see it by globals()).
  3. Whatever operations you perform on i is forwarded to the object it refers to (being int(1) currently) as @valjeanval42 has explained.

Since the objects always know their types, which are the main source of information about what operations they support, python can correctly handle the i variable not whether it is assigned to 1 or '1' (being a str).

Static language like C++ or Java do things vastly differently than a dynamic language like python, as you would have expected. In short, they manage matter of types at compile time while python does it at run time.

Python Keywords, Identifiers and Variables for Beginners, Learn about what are Python keywords, identifiers and variables and Python keyword is a unique programming term intended to perform some action. However, a variable can hold objects of different types as and when required. Search for Learn Python Online Free on the New KensaQ.com


Python - Basic Syntax, Python - Basic Syntax - The Python language has many similarities to Perl, C, and Java. Type the following text at the Python prompt and press the Enter − A Python identifier is a name used to identify a variable, function, class, module or  Python Identifiers are user-defined names to represent a variable, function, class, module or any other object. If you assign some name to a programmable entity in Python, then it is nothing but technically called an identifier. Python language lays down a set of rules for programmers to create meaningful identifiers. Guidelines for Creating Identifiers in Python. 1.


Identifiers in Python - Naming Rules & Best Practices, Today, in this Python tutorial, we will learn about identifiers in Python and how to name them. Moreover Have a look at Python Number Types Python Identifiers. An identifier is a name given to entities like class, functions, variables, etc. It helps to differentiate one entity from another. Rules for writing identifiers. Identifiers can be a combination of letters in lowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or an underscore _.


Python Keywords and Identifiers with examples, In this article, we will discuss Keywords and Identifiers in Python with the help of These keywords have a special meaning and they are used for special purposes in Python programming language. open command prompt (terminal on Mac OS) and type “Python” and hit enter. Variable name is known as identifier. Python Tutorials: Learn Keywords and Identifiers in Python Programming Language Learning Keywords and Identifiers of Python is the next thing that you should learn in Python programming language. In the previous section we have seen the steps to write and test "Hello World" program in Python.