Category: Python

Sometimes, we want to get the cartesian product of a series of lists with Python.

In this article, we’ll look at how to get the cartesian product of a series of lists with Python.

How to get the cartesian product of a series of lists with Python?

To get the cartesian product of a series of lists with Python, we can use the itertools.product method.

For instance, we write:

import itertools

some_lists = [
   [1, 2, 3],
   ['a', 'b'],
   [4, 5]
]
for element in itertools.product(*some_lists):
    print(element)

We call itertools.product with the lists in some_lists spread into it as arguments.

Then we print all the tuples that are in the cartesian products list.

Therefore, we get:

(1, 'a', 4)
(1, 'a', 5)
(1, 'b', 4)
(1, 'b', 5)
(2, 'a', 4)
(2, 'a', 5)
(2, 'b', 4)
(2, 'b', 5)
(3, 'a', 4)
(3, 'a', 5)
(3, 'b', 4)
(3, 'b', 5)

printed.

Conclusion

To get the cartesian product of a series of lists with Python, we can use the itertools.product method.

Sometimes, we want to pad zeroes to a string with Python.

In this article, we’ll look at how to pad zeroes to a string with Python.

How to pad zeroes to a string with Python?

To pad zeroes to a string with Python, we can use the string’s zfill method.

For instance, we write:

n = '5'
print(n.zfill(3))

We call zfill with 3 to pad the string with 0’s before the number to make it 3 digits long.

Therefore, the print function should print '005'.

Conclusion

To pad zeroes to a string with Python, we can use the string’s zfill method.

Sometimes, we want to check if a string is a number with Python.

In this article, we’ll look at how to check if a string is a number with Python.

How to check if a string is a number with Python?

To check if a string is a number with Python, we can use the string’s isdigit method.

For instance, we write:

a = "03523"
print(a.isdigit())

b = "03523abc"
print(b.isdigit())

We call isdigit on a, which is a number string, so the first print call should print True.

Then we call isdigit on b, which isn’t a number string, so the 2nd print call should print False.

Conclusion

To check if a string is a number with Python, we can use the string’s isdigit method.

Sometimes, we want to append to a file with Python.

In this article, we’ll look at how to append to a file with Python.

How to append to a file with Python?

To append to a file with Python, we can open the file with open with append permission.

And then we call write with the string to append to the file.

For instance, we write:

with open("foo.txt", "a") as myfile:
    myfile.write("appended text")

We call open with the path to the file and 'a' to open the file with append permission.

Then we call write with the string to append to the opened file.

Since we use the with statement to open the file, the file will be closed automatically after the append operation is done.

Conclusion

To append to a file with Python, we can open the file with open with append permission.

And then we call write with the string to append to the file.

Sometimes, we want to count the occurrences of a list item with Python.

In this article, we’ll look at how to count the occurrences of a list item with Python.

How to count the occurrences of a list item with Python?

To count the occurrences of a list item with Python, we can use the JavaScript array’s count method.

For instance, we write:

print([1, 2, 3, 4, 1, 4, 1].count(1))

to call count on the array to find the number of times the value 1 is in the array.

Therefore, 3 is printed since 1 appeared 3 times in the array.

Conclusion

To count the occurrences of a list item with Python, we can use the JavaScript array’s count method.