Python test if is array

Python isinstance() Function | Check List, dict, int, array, etc

Python isinstance() function is used to know mid-program which objects belong to which class. If you want to know about the data type number(integer) is belongs to the int class. For that, you have to pass the 2 values in the function.

First value and second guessing class name. See below example, if its matched then result will be True else false.

a = 10 print(isinstance(a, int))

Output: True

Syntax

Parameter

• Object: Required. An object to check part of a class or not.
• Type: class/type/tuple of class or type, against which object is needed to be checked.

Return

• True if the object is an instance or subclass of a class or any element.
• False otherwise

1. Python isinstance list(Array), dict, int and

See the below Working example of isinstance() with Native Types:-

numbers = [11, 22, 33] result = isinstance(numbers, list) print(numbers,'is an instance of the list:-', result) result = isinstance(numbers, dict) print(numbers,'is an instance of dict:-', result) result = isinstance(numbers, (dict, list)) print(numbers,'is an instance of dict or list:-', result) number = 7 result = isinstance(number, list) print(number,'is an instance of the list:-', result) result = isinstance(number, int) print(number,'is an instance of int:-', result)

[11, 22, 33] is an instance of the list:- True
[11, 22, 33] is an instance of dict:- False
[11, 22, 33] is an instance of dict or list:- True
7 is an instance of the list:- False
7 is an instance of int:- True

2. Demonstrating use of isinstance() with objects

class Vehicle: pass class Truck(Vehicle): pass print(isinstance(Vehicle(), Vehicle))

Output: True

Do comment if you have any doubts and suggestions on this tutorial.

Note: This example (Project) is developed in PyCharm 2019.3 (Community Edition)
JRE: 1.8.0
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.13.6
Python 3.7
All Python Programs are in Python 3, so it may change its different from python 2 or upgraded versions.

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How to Check if a Variable is an Array in Python: Complete Guide

Learn how to check if a variable is an array in Python using different methods such as isinstance(), hasattr(), type(), and more. This guide covers NumPy arrays, lists, pandas series, and variable assignment in the current/local/global scope.

• Introduction
• Checking if a variable is a NumPy array
• Checking for scalar array cases
• Subheading 3: Checking if a variable is a list or a pandas series
• Subheading 4: Checking variable assignment in the current/local/global scope
• Subheading 5: Other ways to check if a variable is an array or not
• Other simple code examples for checking variables as arrays in Python
• Conclusion
• How do you check a variable is array or not in Python?
• How do you check if a variable is array or not?
• How do you check the Typeof a variable in Python?
• How do I check if a data type is a list in Python?

If you’re working with Python, chances are you’re working with arrays. When working with arrays, it’s important to know whether a variable is an array or a scalar. In this article, we’ll take a close look at how to determine if a variable is an array or scalar in Python.

Introduction

Python is a highly popular programming language and is widely used in data science projects. Arrays are an important data structure that are frequently used in Python programming. Therefore, it’s essential to know how to determine if a variable is an array or a scalar in Python.

In this article, we’ll cover various methods to check if a variable is an array or not. We’ll discuss the advantages and disadvantages of each method and provide code examples to illustrate how to use them.

Checking if a variable is a NumPy array

NumPy is a popular library for numerical computing in python . To check if a variable is a NumPy array, we can use the isinstance() function.

import numpy as nparr = np.array([1, 2, 3]) if isinstance(arr, np.ndarray): print("Variable is a NumPy array") else: print("Variable is not a NumPy array") 

Variable is a NumPy array 

While NumPy arrays are useful, they can be computationally expensive for small data sets. Therefore, it’s important to consider the advantages and dis advantages of using numpy arrays .

Checking for scalar array cases

In Python, a scalar array is a variable that is an array but has no elements. To check for scalar array cases, we can use the hasattr() function along with the shape attribute.

arr = np.array([]) if hasattr(arr, "shape") and arr.shape == (): print("Variable is a scalar array") else: print("Variable is not a scalar array") 

Variable is a scalar array 

It’s important to understand the difference between scalar arrays and non-scalar arrays. Scalar arrays can be used to store metadata or act as placeholders, while non-scalar arrays contain elements.

Subheading 3: Checking if a variable is a list or a pandas series

In addition to NumPy arrays, lists and pandas series are also frequently used in Python. To check if a variable is a list or a pandas series, we can use the isinstance() function.

import pandas as pdlst = [1, 2, 3] ser = pd.Series([1, 2, 3])if isinstance(lst, (list, pd.core.series)): print("Variable is a list or a pandas series") else: print("Variable is not a list or a pandas series") 

Variable is a list or a pandas series 

It’s important to understand the differences between lists and pandas series, as they have different properties and are used for different purposes.

Subheading 4: Checking variable assignment in the current/local/global scope

Python has built-in functions to check if a variable is assigned in the current, local, or global scope. These functions are locals() , globals() , and vars() .

def test(): x = 1 if "x" in locals(): print("Variable 'x' is assigned in local scope") if "x" in globals(): print("Variable 'x' is assigned in global scope")test() 

Variable 'x' is assigned in local scope 

It’s important to understand the differences between current, local, and global scopes, as they affect how variables are accessed and modified.

Subheading 5: Other ways to check if a variable is an array or not

In addition to the previous methods, there are several other ways to check if a variable is an array or not.

To check if a variable is None , we can use the not a is None syntax instead of not a .

To check if a variable is an exact type of list, we can use type(a) is list instead of using == .

To check if an element is present in a list, we can use the in and not in operators.

To check if a variable is a list, we can use the type() and isinstance() functions.

Other simple code examples for checking variables as arrays in Python

In Python , python check if variable is array code example

isinstance([0, 10, 20, 30], list) # True isinstance(50, list) # False

Conclusion

In this article, we covered various methods to check if a variable is an array or scalar in Python. We discussed the advantages and disadvantages of each method and provided code examples to illustrate how to use them.

It’s important to understand how to check if a variable is an array or not, as it’s a fundamental concept in Python programming. By using the methods outlined in this article, you can ensure that your code is accurate and efficient.

If you’re interested in learning more about Python programming language and data science, there are many resources available online.

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Python: Check if Variable is a List

Python is a dynamically typed language, and the variable data types are inferred without explicit intervention by the developer.

If we had code that needed a list but lacked type hints, which are optional, how can we avoid errors if the variable used is not a list?

In this tutorial, we’ll take a look at how to check if a variable is a list in Python, using the type() and isinstance() functions, as well as the is operator:

Developers usually use type() and is , though these can be limited in certain contexts, in which case, it’s better to use the isinstance() function.

Check if Variable is a List with type()

The built-in type() function can be used to return the data type of an object. Let’s create a Dictionary, Tuple and List and use the type() function to check if a variable is a list or not:

grocery_list = ["milk", "cereal", "ice-cream"] aDict = "username": "Daniel", "age": 27, "gender": "Male"> aTuple = ("apple", "banana", "cashew") # Prints the type of each variable print("The type of grocery_list is ", type(grocery_list)) print("The type of aDict is ", type(aDict)) print("The type of aTuple is ", type(aTuple)) 

The type of grocery_list is class 'list'> The type of aDict is class 'dict'> The type of aTuple is class 'tuple'> 

Now, to alter code flow programmatically, based on the results of this function:

a_list = [1, 2, 3, 4, 5] # Checks if the variable "a_list" is a list if type(a_list) == list: print("Variable is a list.") else: print("Variable is not a list.") 

Check if Variable is a List with is Operator

The is operator is used to compare identities in Python. That is to say, it’s used to check if two objects refer to the same location in memory.

The result of type(variable) will always point to the same memory location as the class of that variable . So, if we compare the results of the type() function on our variable with the list class, it’ll return True if our variable is a list.

Let’s take a look at the is operator:

a_list = [1, 2, 3, 4, 5] print(type(a_list) is list) 

Since this might look off to some, let’s do a sanity check for this approach, and compare the IDs of the objects in memory as well:

print("Memory address of 'list' class:", id(list)) print("Memory address of 'type(a_list)':", id(type(a_list))) 

Now, these should return the same number:

Memory address of 'list' class: 4363151680 Memory address of 'type(a_list)': 4363151680 

Note: You’ll need to keep any subtypes in mind if you’ve opted for this approach. If you compare the type() result of any list sub-type, with the list class, it’ll return False , even though the variable is-a list, although, a subclass of it.

This shortfall of the is operator is fixed in the next approach — using the isinstance() function.

Check if Variable is a List with isinstance()

The isinstance() function is another built-in function that allows you to check the data type of a variable. The function takes two arguments — the variable we’re checking the type for, and the type we’re looking for.

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This function also takes sub-classes into consideration, so any list sub-classes will also return True for being an instance of the list .

Let’s try this out with a regular list and a UserList from the collections framework:

from collections import UserList regular_list = [1, 2, 3, 4, 5] user_list = [6, 7, 8, 9, 10] # Checks if the variable "a_list" is a list if isinstance(regular_list, list): print("'regular_list' is a list.") else: print("'regular_list' is not a list.") # Checks if the variable "a_string" is a list if isinstance(user_list, list): print("'user_list' is a list.") else: print("'user_list' is not a list.") 

Running this code results in:

'regular_list' is a list. 'user_list' is a list. 

Conclusion

Python is a dynamically typed language, and sometimes, due to user-error, we might deal with an unexpected data type.

In this tutorial, we’ve gone over three ways to check if a variable is a list in Python — the type() function, the is operator and isinstance() function.

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