for i j in python

The Python expression for i, j in XXX allows you to iterate over an iterable XXX of pairs of values. For example, to iterate over a list of tuples, this expression captures both tuple values in the loop variables i and j at once in each iteration.

Here’s an example:

for i, j in [('Alice', 18), ('Bob', 22)]: print(i, 'is', j, 'years old')

Output:

Alice is 18 years old

Bob is 22 years old

Notice how the first loop iteration captures i='Alice' and j=18, whereas the second loop iteration captures i='Bob' and j=22.

for i j in enumerate python

The Python expression for i, j in enumerate(iterable) allows you to loop over an iterable using variable i as a counter (0, 1, 2, …) and variable j to capture the iterable elements.

Here’s an example where we assign the counter values i=0,1,2 to the three elements in lst:

lst = ['Alice', 'Bob', 'Carl']

for i, j in enumerate(lst): print(i, j)

Output:

0 Alice

1 Bob

2 Carl

Notice how the loop iteration capture:

• i=0 and j='Alice',
• i=1 and j='Bob', and
• i=2 and j='Carl'.

Learn More: The enumerate() function in Python.

for i j in zip python

The Python expression for i, j in zip(iter_1, iter_2) allows you to align the values of two iterables iter_1 and iter_2 in an ordered manner and iterate over the pairs of elements. We capture the two elements at the same positions in variables i and j.

Here’s an example that zips together the two lists [1,2,3] and [9,8,7,6,5].

for i, j in zip([1,2,3], [9,8,7,6,5]): print(i, j)

Output:

1 9

2 8

3 7

Learn More: The zip() function in Python.

for i j in list python

The Python expression for i, j in list allows you to iterate over a given list of pairs of elements (list of tuples or list of lists). In each iteration, this expression captures both pairs of elements at once in the loop variables i and j.

Here’s an example:

for i, j in [(1,9), (2,8), (3,7)]: print(i, j)

Output:

1 9

2 8

3 7

for i j k python

The Python expression for i, j, k in iterable allows you to iterate over a given list of triplets of elements (list of tuples or list of lists). In each iteration, this expression captures all three elements at once in the loop variables i and j.

Here’s an example:

for i, j, k in [(1,2,3), (4,5,6), (7,8,9)]: print(i, j, k)

Output:

1 2 3

4 5 6

7 8 9

for i j in a b python

Given two lists a and b, you can iterate over both lists at once by using the expression for i,j in zip(a,b).

Given one list ['a', 'b'], you can use the expression for i,j in enumerate(['a', 'b']) to iterate over the pairs of (identifier, list element) tuples.

Summary

The Python for loop is a powerful method to iterate over multiple iterables at once, usually with the help of the zip() or enumerate() functions.

for i, j in zip(range(10), range(10)): # (0,0), (1,1), ..., (9,9)

If a list element is an iterable by itself, you can capture all iterable elements using a comma-separated list when defining the loop variables.

for i,j,k in [(1,2,3), (4,5,6)]: # Do Something

Problem Formulation

Challenge: How to design a regular expression pattern that matches whitespace characters such as the empty space ' ' and the tabular character '\t', but not the newline character '\n'?

An example of this would be to replace all whitespaces (except newlines) between a space-delimited file with commas to obtain a CSV.

Method 1: Use Character Class

The character class pattern [ \t] matches one empty space ' ' or a tabular character '\t', but not a newline character. If you want to match an arbitrary number of empty spaces except for newlines, append the plus quantifier to the pattern like so: [ \t]+.

Here’s an example where you replace all separating whitespace (except newline) with a comma to receive a CSV formatted output:

import re txt = 'a \t b c\nd e f'

csv_txt = re.sub('[ \t]+', ',', txt)

print(csv_txt)

Output:

a,b,c

d,e,f

Why the space in the pattern [ \t]?

The reason there’s a space in the pattern is to match the empty space. The character class essentially is an OR relationship, i.e., one item within the character class is matched. For the given pattern, it matches either the empty space ' ' or the tabular character '\t'.

Learn More: Character Class (Character Set) — The Ultimate Guide for Python

Method 2: Match Individual Different Whitespace Characters

The previous method only matches the horizontal tab (U+0009) and breaking space (U+0020) characters. If you want more fine-grained control about which whitespace characters to match and which not, you can use the following baseline approach.

The following list of Unicode whitespace characters UNICODE_WHITESPACES contains all major whitespace variants you may want to check your string for. You can generate a character class using the string expression '[' + ''.join(UNICODE_WHITESPACES) + ']'.

Here’s a variant that finds all matches of whitespace characters in a given text:

import re UNICODE_WHITESPACES = [ "\u0009", # character tabulation "\u000a", # line feed "\u000b", # line tabulation "\u000c", # form feed "\u000d", # carriage return "\u0020", # space "\u0085", # next line "\u00a0", # no-break space "\u1680", # ogham space mark "\u2000", # en quad "\u2001", # em quad "\u2002", # en space "\u2003", # em space "\u2004", # three-per-em space "\u2005", # four-per-em space "\u2006", # six-per-em space "\u2007", # figure space "\u2008", # punctuation space "\u2009", # thin space "\u200A", # hair space "\u2028", # line separator "\u2029", # paragraph separator "\u202f", # narrow no-break space "\u205f", # medium mathematical space "\u3000", # ideographic space

] txt = ' \t\n\r'

pattern = '[' + ''.join(UNICODE_WHITESPACES) + ']'

matches = re.findall(pattern, txt)

print(matches)

# [' ', '\t', '\n', '\r']

Of course, you can restrict this to only contain whitespaces that are not newline-related.

Method 3: Match Individual Different Whitespaces Except Newlines

The following code snippet uses the UNICODE_WHITESPACES constant but comments out the newline whitespaces so that newline-related characters such as '\n' and '\r' are not matched anymore!

import re UNICODE_WHITESPACES = [ "\u0009", # character tabulation # "\u000a", # line feed "\u000b", # line tabulation "\u000c", # form feed # "\u000d", # carriage return "\u0020", # space # "\u0085", # next line "\u00a0", # no-break space "\u1680", # ogham space mark "\u2000", # en quad "\u2001", # em quad "\u2002", # en space "\u2003", # em space "\u2004", # three-per-em space "\u2005", # four-per-em space "\u2006", # six-per-em space "\u2007", # figure space "\u2008", # punctuation space "\u2009", # thin space "\u200A", # hair space # "\u2028", # line separator # "\u2029", # paragraph separator "\u202f", # narrow no-break space "\u205f", # medium mathematical space "\u3000", # ideographic space

] txt = ' \t\n\r'

pattern = '[' + ''.join(UNICODE_WHITESPACES) + ']'

matches = re.findall(pattern, txt)

print(matches)

# [' ', '\t']

Of course, you can comment out the individual whitespace Unicode characters you don’t want to match as required by your own application.

[] 100%

Problem Formulation and Solution Overview

In this article, you’ll learn how to configure and display a progress bar.

A progress bar is commonly used in Python or, for that matter, any other programming language to show the user an application’s progress. For example, an installation, a transferring of files, or any other commands.

The Finxter Academy recommends implementing this to visually display to the user what is happening behind the scenes.

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Question: How would we write code to display a progress bar?

We can accomplish this task by one of the following options:

• Method 1: Use a for loop
• Method 2: Use apytl library Bar().drawbar() function
• Method 3: Use alive-progress
• Method 4: Use tqdm
• Method 5: Use progress

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Method 1: Use a For Loop

This method imports the time and sys libraries combined with a for loop to display a custom progress bar output on a single line.

from time import sleep

import sys for x in range(0,21): sys.stdout.write('\r') sys.stdout.write("[%-20s] %d%%" % (''*x, 5*x)) sys.stdout.flush() sleep(0.75)

Above imports, the time library to call the sleep command and the sys library to write the contents to the terminal.

Next, a for loop is instantiated. This loop uses the range function to set the start position (0 by default) and the stop position (21-1). Inside this loop, the following occurs:

• The first line uses a carriage return (\r) to start the code on a new line.
• The following line determines how the progress bar appears by:
  
  • Left-aligning the emoji(s) inside the square brackets [%-20s].
  • Configuring the progress percentage %d%%" % (example 15%).
  • Determining the visual emoji progress ('😁'*x, 5*x).
• Then sys.stdout.flush() writes everything in the buffer to the terminal.
• The code pauses for the stated period (0.75).

The loop continues until 100% has been attained. Below is the end result.

[] 100%

Note: Any emoji or another symbol can be substituted for the above selection.

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Method 2: Use apytl Library

This method imports the time and apytl libraries to generate a custom progress bar.

To run this code error-free, install the required library. Click here for installation instructions.

import time

import apytl total_iterations = 10 for index, value in enumerate(range(total_iterations)): apytl.Bar().drawbar(value, total_iterations, fill='*') time.sleep(0.75)

Above imports the time library to call the sleep command and the apytl library to display the progress bar.

Next, the total number of iterations to carry out is declared as 10 and saved to total_iterations.

To understand what is going on in the for loop, let’s write some test code to see what the values of index, value and total_iterations are doing:

total_iterations = 10 for index, value in enumerate(range(total_iterations)): print(index, value, total_iterations)

As you can see from the output, the index and value variables count from 0 (range default start position) to the stop position of 9 (10-1). Notice the value of total_iterations does not change.

0 0 10 1 1 10 2 2 10 3 3 10 4 4 10 5 5 10 6 6 10 7 7 10 8 8 10 9 9 10

Referring back to the code directly below the Method 2 heading, the next line is: apytl.Bar().drawbar(value, total_iterations, fill='*').

This function is passed three (3) arguments:

• The variable value, which you can see from the above, increments by one (1) each iteration.
• The variable total_iterations, which remains constant at 10.
• The fill value. This example uses the asterisk (*) character. However, feel free to use an emoji or other symbol.

Progress |***********************************| 100.0% Complete

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Method 3: Use alive-progress

The alive-progress library moves progress bars to the next level! With its many display options, it’s a must-a-try!

To run this code error-free, install the required library. Click here for installation instructions.

from alive_progress import alive_bar

from time import sleep for x in range(10): with alive_bar(x, bar='solid') as bar: for i in range(x): sleep(.001) bar()

Above imports the alive-progress library to use the progress bar and the time library to call the sleep command.

Next, a for loop is instantiated. This loop uses the range function to set the stop position at 9 (10-1). Inside this loop, the following occurs:

• The alive_bar is called and passed the argument x and the bar type. For this example, solid was selected.
  
  • A new for loop is instantiated and loops through range passing x as an argument.
  • The code halts (sleep) for the stated period (.001).
  • The bar is output to the terminal each iteration.

The loop continues until 100% has been attained.

<■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 0 in 0.0s (0.00/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 1/1 [100%] in 0.0s (333.28/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 2/2 [100%] in 0.0s (62.48/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 3/3 [100%] in 0.0s (63.96/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 4/4 [100%] in 0.1s (62.39/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 5/5 [100%] in 0.1s (63.32/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 6/6 [100%] in 0.1s (64.84/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 7/7 [100%] in 0.1s (63.79/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 8/8 [100%] in 0.1s (63.53/s) <■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■> 9/9 [100%] in 0.1s (64.09/s)

Note: To view a list of all available progress bars, click here.

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Method 4: Use tqdm

A simple yet elegant progress bar, tqdm is a must-see!

To run this code error-free, install the required library. Click here for installation instructions.

from tqdm import tqdm

from time import sleep for i in tqdm(range(100)): sleep(0.02)

Above imports the tqdm library for the progress bar and the time library to call the sleep() command.

Next, a for loop is instantiated. This loop uses the tqdm library with the range function to set the stop position at 99 (100-1). Inside this loop, the following occurs:

The progress bar displays on one line. Each iteration increases the progress by a percentage.

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Method 5: Use progress Library

This method uses the progress library to display a progress bar. This library has many fun options to select from.

To run this code error-free, install the required library. Click here for installation instructions.

from time import sleep

from progress.spinner import MoonSpinner with MoonSpinner('Processing…') as bar: for i in range(100): sleep(0.02) bar.next()

Above imports the time library to call the sleep command and the progress library to display a progress bar, specifically the MoonSpinner.

The following code displays the word Processing... at the terminal, and the MoonSpinner rotates, sleeps, and continues until the value of the range stop position (100-1) is attained.

Processing…◑

Note: Spend some time on this library page to test the different types of progress bars.

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Summary

There is so much more to Python Progress Bars than was covered in this article. May we suggest you take time to delve into each method outlined above to determine the best one for your requirements.

Happy Coding!

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Programming Humor – Python