Author: John Au-Yeung

Sometimes, we want to check if a variable exists with Python.

In this article, we’ll look at how to check if a variable exists with Python.

How to check if a variable exists with Python?

To check if a variable exists with Python, we can use the locals function to check if a local variables exists.

We can use the globals function to check if a global variable exists.

And we can use hasattr to check if an object has the given attribute.

For instance, we write:

bar = 1


def baz():
    foo = 1
    if 'foo' in locals():
        print('foo exists')


baz()

if 'bar' in globals():
    print('bar exists')


class A:
    attr = 1


obj = A()
if hasattr(obj, 'attr'):
    print('attr exists')

We have the bar global variable.

And we have the baz function with the foo local variable.

In baz, we check if foo is in baz using if 'foo' in locals().

We check if bar is a global variable that’s defined with if 'bar' in globals().

Also, we have an A class with the attr attribute.

We instantiate that and assign the A instance to obj.

Then we check if attr is in obj with if hasattr(obj, 'attr').

Since all of the exist, we should see:

foo exists
bar exists
attr exists

printed.

Conclusion

To check if a variable exists with Python, we can use the locals function to check if a local variables exists.

We can use the globals function to check if a global variable exists.

And we can use hasattr to check if an object has the given attribute.

Sometimes, we want to reverse a list in Python.

In this article, we’ll look at how to reverse a list in Python.

How to reverse a list in Python?

To reverse a list in Python, we can use the reversed function.

For instance, we write:

array = [0, 10, 20, 40]
l = list(reversed(array))
print(l)

We call reversed with array to return an iterator with the entries in array reversed.

Then we convert that back to a list with list.

Therefore, l is [40, 20, 10, 0].

Conclusion

To reverse a list in Python, we can use the reversed function.

Sometimes, we want to remove duplicates in lists in Python.

In this article, we’ll look at how to remove duplicates in lists in Python.

How to remove duplicates in lists in Python?

To remove duplicates in lists in Python, we can convert the list to a set and then back to a list with the set and list functions respectively.

For instance, we write:

t = [1, 2, 3, 1, 2, 5, 6, 7, 8]
s = list(set(t))
print(s)

We call set with t to return a set with t‘s elements but without the duplicates.

Then we call list to convert the set back to a list and assign it to s.

Therefore, s is [1, 2, 3, 5, 6, 7, 8].

Conclusion

To remove duplicates in lists in Python, we can convert the list to a set and then back to a list with the set and list functions respectively.

Sometimes, we want to determine if an object is iterable in Python.

In this article, we’ll look at how to determine if an object is iterable in Python.

How to determine if an object is iterable in Python?

To determine if an object is iterable in Python, we can use the collections module.

For instance, we write:

from collections.abc import Iterable

x = 100
y = [1, 2]
x_iterable = isinstance(x, Iterable)
y_iterable = isinstance(y, Iterable)

print(x_iterable)
print(y_iterable)

We import Iterable from the collections.abc module.

Then we call isinstance with the variables we want to check and Iterable to check if x and y are iterable.

Therefore, x_iterable is False and y_iterable is True since x is an integer and y is an array.

Conclusion

To determine if an object is iterable in Python, we can use the collections module.

Sometimes, we want to create multiline comments in Python.

In this article, we’ll look at how to create multiline comments in Python.

How to create multiline comments in Python?

To create multiline comments in Python, we can enclose the comment with ''' or create consecutive single line comments.

For instance, we write:

'''
This is a multiline
comment.
'''

to add a multiline comment.

Or, we can add consecutive single line comments with:

# This is a multiline
# comment.

Conclusion

To create multiline comments in Python, we can enclose the comment with ''' or create consecutive single line comments.