'id' is a bad variable name in Python

Asked by At

Why is it bad to name a variable id in Python?

8 Answers

115
Kevin Little On Best Solutions

id() is a fundamental built-in:

Help on built-in function id in module __builtin__:

id(...)

    id(object) -> integer

    Return the identity of an object.  This is guaranteed to be unique among
    simultaneously existing objects.  (Hint: it's the object's memory
    address.)

In general, using variable names that eclipse a keyword or built-in function in any language is a bad idea, even if it is allowed.

1
ahockley On

Because it's the name of a builtin function.

4
Toni Ruža On

It's bad to name any variable after a built in function. One of the reasons is because it can be confusing to a reader that doesn't know the name is overridden.

1
Haoest On

'id' is a built-in method in Python. Assigning a value to 'id' will overwrite the method. It is best to use either an identifier before as in "some_id" or use it in a different capitalization method.

The built in method takes a single parameter and returns an integer for the memory address of the object that you passed.

>>>id(1)

9787760

>>>x = 1

>>>id(x)

9787760

38
Sebastian Rittau On

I might say something unpopular here: id() is a rather specialized built-in function that is rarely used in business logic. Therefore I don't see a problem in using it as a variable name in a tight and well-written function, where it's clear that id doesn't mean the built-in function.

-6
Kitty On

Because python is a dynamic language, it's not usually a good idea to give a variable and a function the same name. id() is a function in python, so it's recommend not to use a variable named id. Bearing that in mind, that applies to all functions that you might use... a variable shouldn't have the same name as a function.

45
Nathan Shively-Sanders On

id is a built-in function that gives the memory address of an object. If you name one of your functions id, you will have to say __builtins__.id to get the original. Renaming id globally is confusing in anything but a small script.

However, reusing built-in names as variables isn't all that bad as long as the use is local. Python has a lot of built-in functions that (1) have common names and (2) you will not use much anyway. Using these as local variables or as members of an object is OK because it's obvious from context what you're doing:

Example:

def numbered(filename):
  file = open(filename)
  for i,input in enumerate(file):
    print "%s:\t%s" % (i,input)
  file.close()

Some built-ins with tempting names:

  • id
  • file
  • list
  • map
  • all, any
  • complex
  • dir
  • input
  • slice
  • buffer
38
DavidRR On

In PEP 8 - Style Guide for Python Code, the following guidance appears in the section Descriptive: Naming Styles :

  • single_trailing_underscore_ : used by convention to avoid conflicts with Python keyword, e.g.

    Tkinter.Toplevel(master, class_='ClassName')

So, to answer the question, an example that applies this guideline is:

id_ = 42

Including the trailing underscore in the variable name makes the intent clear (to those familiar with the guidance in PEP 8).