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Nov 26, 2015 · Python has nothing called pointers, but your code works as written. Function are first-class objects, assigned to names, and used as any other value. You can use this to implement a Strategy pattern, for example: def the_simple_way(a, b): # blah blah. def the_complicated_way(a, b): # blah blah. def foo(way):
Using the builtin ctypes module, you can create real C-style pointers in Python. If you are unfamiliar with ctypes, then you can take a look at Extending Python With C Libraries and the “ctypes” Module. The real reason you would use this is if you needed to make a function call to a C library that requires a pointer.
- Terminology
- Python's Variables Are Pointers, Not Buckets
- Assignments Point A Variable to An Object
- The 2 Types of "Change" in Python
- Equality Compares Objects and Identity Compares Pointers
- There's No Exception For Immutable Objects
- Data Structures Contain Pointers
- Function Arguments Act Like Assignment Statements
- Copies Are Shallow and That's Usually Okay
- Summary
Let's start with by introducing some terminology.The last few definitions likely won't make sense until we define them in more detail later on. Object (a.k.a. value): a "thing".Lists, dictionaries, strings, numbers, tuples, functions, and modules are all objects."Object" defies definition because everything is an object in Python. Variable (a.k.a. ...
Variables in Python are not buckets containing things; they're pointers (they pointto objects). The word "pointer" may sound scary, but a lot of that scariness comes from related concepts (e.g. dereferencing) which aren't relevant in Python.In Python a pointer just represents the connection between a variable and an objects. Imagine variables livin...
Assignment statements point a variable to an object.That's it. If we run this code: The state of our variables and objects would look like this: Note that numbers and numbers2 point to the same object.If we changethat object, both variables will seem to "see" that change: That strangeness was all due to this assignment statement: Assignment stateme...
Python has 2 distinct types of "change": 1. Assignment changes a variable (it changes whichobject it points to) 2. Mutationchanges an object (which any number of variables might point to) The word "change" is often ambiguous.The phrase "we changed x" could mean "we re-assigned x" or it might mean "we mutated the object xpoints to". Mutations change...
Python's == operator checks that two objects represent the same data (a.k.a. equality): Python's is operator checks whether two objects are the same object (a.k.a. identity): The variables my_numbers and your_numbers point to objects representing the same data, but the objects they point to are not the same object. So changing one object doesn't ch...
But wait, modifying a number doesn'tchange other variables pointing to the same number, right? Well, modifying a number is not possible in Python.Numbers and strings are both immutable, meaning you can't mutate them.You cannot changean immutable object. So what about that +=operator above?Didn't that mutate a number?(It didn't.) With immutable obje...
Like variables, data structures don't contain objects, they contain pointers to objects. Let's say we make a list-of-lists: And then we make a variable pointing to the second list in our list-of-lists: The state of our variables and objects now looks like this: Our row variable points to the same object as index 1 in our matrixlist: So if we mutate...
Function calls also perform assignments. If you mutate an object that was passed-in to your function, you've mutated the original object: But if you reassign a variable to a different object, the original object will not change: We're reassigning the items variable here.That reassignment changes which object the itemsvariable points to, but it does...
Need to copy a list in Python? You could call the copymethod (if you're certain your iterable is a list): Or you could pass it to the list constructor (this works on any iterable): Both of these techniques make a new list which points to the same objectsas the original list. The two lists are distinct, but the objects within them are the same: Sinc...
Variables in Python are not buckets containing things; they're pointers (they pointto objects). Python's model of variables and objects boils down to two primary rules: 1. Mutationchanges an object 2. Assignmentpoints a variable to an object As well as these corollary rules: 1. Reassigning a variable points it to a different object, leaving the ori...
The assignment operator = in Python automatically creates and assigns a pointer to the variable. Example: l = [1,2,3,4] The above statement creates a list object and points a pointer to it called “l”. If you assign the same list object both to two different variables m and l, they will point to the same memory location. #Assign.
Jan 8, 2024 · Understanding the difference between these two types is crucial in Python programming, as it affects how variables and functions interact with the data. Passing Arguments to Functions. One of the key aspects of understanding Python’s behaviour is how it handles the passing of arguments to functions.
Jun 13, 2020 · Pointers Using ctypes. We can create real pointers in Python using the built in ctype modules. To start, store your functions that use pointers in a .c file and compile it. Write the below function into your .c file. void add(int *a) { *a += 10; } Assume our file name is pointers.c. Run the below commands.
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By using function pointers, we can write more modular and reusable code. Understanding function pointers in Python 3 is essential for any programmer looking to leverage the full power of the language. For more information on function pointers in Python 3, you can refer to the following resources: Python 3 Documentation: Defining Functions
