Python Basics: Number Reversal, Docstrings, Encoding, String Rotation, Progress Bar, File Output, and List Merging

The article encourages daily Python practice, offering short coding exercises to reinforce basic programming skills.

Reverse Number – Convert a three‑digit integer (e.g., 789) to its reversed form (987) by extracting hundreds, tens, and units. The solution is demonstrated with the following function:

def reverse_number(number):
    baiwei = int(number/100)
    shiwei = int(number%100/10)
    gewei = int(number%10)
    return gewei*100 + shiwei*10 + baiwei

new_number = reverse_number(789)
print(new_number)

Class Docstring – Add documentation to a newly created class using triple quotes. The docstring can be accessed via ClassName.__doc__ :

class My_Class(object):
    """你好"""

print(My_Class.__doc__)

Setting Python File Encoding – Python source files default to UTF‑8, but an explicit encoding declaration can be added on the first or second line using a comment that matches the regular expression coding[=:]\s*([-\w.]+) . Examples:

# -*- coding:utf-8 -*-
# -*- coding:UTF-8 -*-

Rotate String – Given a string and an integer offset, rotate the string accordingly (e.g., abcde with offset 3 becomes cdeab ). The implementation uses slicing:

def reverse_str(my_str, offset):
    if offset == 0:
        return my_str
    left = my_str[:len(my_str)-offset]
    right = my_str[len(my_str)-offset:]
    return right + left

Console Progress Bar – Display a progress bar in the console by formatting a string with completed ( > ) and remaining ( / ) characters, using ljust() for padding. A loop updates the bar in real time:

# Print a line of progress symbols
progress_str = ">" * 100
print(progress_str)

import time
for i in range(0, 11):
    time.sleep(0.3)
    current = i/10
    progress_str = '{0:s}{1:.0%}'.format((int(current*10)*'>').ljust(10, '/'), current)
    print(f'\r{progress_str}', end='')

Redirecting print to a File – Use the file parameter of print() to write output directly to a file instead of the console:

file = open('runtime.log', 'a+', encoding='utf-8')
print('测试日志', file=file)

Merge Two Lists – Combine two lists and sort the result using bubble sort to maintain order. The following function merges and sorts the lists, then prints the merged list:

def merge(l1, l2):
    my_list = l1 + l2
    n = len(my_list)
    for i in range(n):
        for j in range(0, n - i - 1):
            if my_list[j] > my_list[j + 1]:
                my_list[j], my_list[j + 1] = my_list[j + 1], my_list[j]
    print(my_list)

if __name__ == '__main__':
    my_list1 = [4, 2, 6]
    my_list2 = [1, 3]
    merge(my_list1, my_list2)