Category: Python Answers

Sometimes, we want to get the index of the returned max or min item using max()/min() on a list with Python.

In this article, we’ll look at how to get the index of the returned max or min item using max()/min() on a list with Python.

How to get the index of the returned max or min item using max()/min() on a list with Python?

To get the index of the returned max or min item using max()/min() on a list with Python, we can use the values.__getitem__ method as the value of the key parameter of min.

For instance, we write:

values = [1, 2, 3, 4, 5]
index_min = min(range(len(values)), key=values.__getitem__)
print(index_min)

We call min with range(len(values)) to get the min index of the item with the lowest value in the values list.

And we set key to values.__getitem__ to get the value from the index in the range(len(values)) generator so we can use the values in the values list for comparison.

Therefore, index_min is 0.

Conclusion

To get the index of the returned max or min item using max()/min() on a list with Python, we can use the values.__getitem__ method as the value of the key parameter of min.

Sometimes, we want to get the home directory in Python in a cross-platform way.

In this article, we’ll look at how to get the home directory in Python in a cross-platform way.

What is the correct cross-platform way to get the home directory in Python?

To get the home directory in Python in a cross-platform way, we can use the pathlib module.

For instance, we write:

from pathlib import Path

home = str(Path.home())
print(home)

to call Path.home to return the home directory value as an object.

Then we can convert it to a string with str and return it.

Therefore, home is something like '/home/runner'.

Conclusion

To get the home directory in Python in a cross-platform way, we can use the pathlib module.

Sometimes, we want to create a Caesar cipher function in Python.

In this article, we’ll look at how to create a Caesar cipher function in Python.

How to create a Caesar cipher function in Python?

To create a Caesar cipher function in Python, we can create our own function to map the string characters to the new characters.

For instance, we write:

import string


def caesar(plaintext, shift):
    alphabet = string.ascii_lowercase
    shifted_alphabet = alphabet[shift:] + alphabet[:shift]
    table = str.maketrans(alphabet, shifted_alphabet)
    return plaintext.translate(table)


print(caesar('foobar', 2))

to define the caesar function that takes the plaintext to encrypt and the shift to specify the number of positions to shift each character in the character set.

We get all the ASCII alphabet characters with string.ascii_lowercase.

Then we shift the alphabet with alphabet[shift:] + alphabet[:shift].

Next, we map each character to the new characters with str.maketrans(alphabet, shifted_alphabet).

And then we return the encrypted string with plaintext.translate(table).

Therefore, the print output should be 'hqqdct' since we shifted each character 3 positions to the right in the alphabet table.

Conclusion

To create a Caesar cipher function in Python, we can create our own function to map the string characters to the new characters.

Sometimes, we want to rewrite multiple lines in the console with Python.

In this article, we’ll look at how to rewrite multiple lines in the console with Python.

How to rewrite multiple lines in the console with Python?

To rewrite multiple lines in the console with Python, we can use sys.stdout.write to move up the cursor to delete a line.

For instance, we write:

import sys
import time
from collections import deque

queue = deque([], 3)
for t in range(20):
    time.sleep(0.5)
    s = "update %d" % t
    for _ in range(len(queue)):
        sys.stdout.write("\x1b[1A\x1b[2K")
    queue.append(s)
    for i in range(len(queue)):
        sys.stdout.write(queue[i] + "\n")

We have a for loop and we loop from 0 to 19.

In the loop, we call time.sleep to pause for 0.5 seconds.

Then we loop through from 0 to the length of the queue minus 1 with another for loop and erase the previous line by writing:

sys.stdout.write("\x1b[1A\x1b[2K")

Next, we call queue.append to append the s string.

And then we call sys.stdout.write(queue[i] + "\n") to update the text again.

Conclusion

To rewrite multiple lines in the console with Python, we can use sys.stdout.write to move up the cursor to delete a line.

Sometimes, we want to rank items in an array using Python NumPy, without sorting array twice.

In this article, we’ll look at how to rank items in an array using Python NumPy, without sorting array twice.

How to rank items in an array using Python NumPy, without sorting array twice?

To rank items in an array using Python NumPy, without sorting array twice, we can use the argsort method.

For instance, we write:

import numpy

array = numpy.array([4, 2, 7, 1])
order = array.argsort()
ranks = order.argsort()
print(order)
print(ranks)

We create a NumPy array with numpy.array with a list of numbers.

Then we call array.argsort to get the order of each item in the array.

And we call order.argsort to get the ranking of each value in the array.

Therefore, we see:

[3 1 0 2]
[2 1 3 0]

printed.

Conclusion

To rank items in an array using Python NumPy, without sorting array twice, we can use the argsort method.