Master Python String & List Tricks: Reverse, Palindromes, Unique Elements & More

String Operations

1. Reverse a string

# Method 1
s = 'hello  world'
print(s[::-1])

# Method 2
from functools import reduce
print(reduce(lambda x, y: y + x, s))

2. Check if a string is a palindrome

Use string reversal to determine palindrome status.

s1 = 'abccba'
s2 = 'abcde'

def func(s):
    if s == s[::-1]:
        print('Palindrome')
    else:
        print('Not palindrome')

func(s1)
func(s2)

3. Find unique characters in a string

Use set to deduplicate.

# String example
s1 = 'wwweeerftttg'
print(''.join(set(s1)))  # e.g., ftgwer

# List example
l1 = [2, 4, 5, 6, 7, 1, 2]
print(list(set(l1)))  # [1, 2, 4, 5, 6, 7]

4. Compare if strings contain the same elements

Elements are considered the same if they have identical counts regardless of order.

from collections import Counter

s1, s2, s3 = 'asdf', 'fdsa', 'sfad'
c1, c2, c3 = Counter(s1), Counter(s2), Counter(s3)

if c1 == c2 and c2 == c3:
    print('Match')

List Operations

1. Flatten a nested list

from iteration_utilities import deepflatten
l = [[12, 5, 3], [2, 4, [5], [6, 9, 7]]]
print(list(deepflatten(l)))

2. Decompose an iterable of arbitrary length

first, *middle, last = grades  # * unpacks the middle part

3. Get the N largest or smallest elements

import heapq

nums = [1, 8, 2, 23, 7, -4, 18, 23, 42, 37, 2]
print(heapq.nlargest(3, nums))   # [42, 37, 23]
print(heapq.nsmallest(3, nums))  # [-4, 1, 2]

portfolio = [
    {'name': 'IBM', 'shares': 100, 'price': 91.1},
    {'name': 'AAPL', 'shares': 50, 'price': 543.22},
    {'name': 'FB', 'shares': 200, 'price': 21.09},
    {'name': 'HPQ', 'shares': 35, 'price': 31.75},
    {'name': 'YHOO', 'shares': 45, 'price': 16.35},
    {'name': 'ACME', 'shares': 75, 'price': 115.65},
]

cheap = heapq.nsmallest(3, portfolio, key=lambda s: s['price'])

Other Utilities

1. Check object memory usage

import sys

s1 = 'a'
s2 = 'aaddf'
n1 = 32
print(sys.getsizeof(s1))  # 50
print(sys.getsizeof(s2))  # 54
print(sys.getsizeof(n1))  # 28

2. Print variations

# Print to a file
with open('somefile.txt', 'rt') as f:
    print('Hello World!', file=f)

# Custom separator and end
print('GKY', 1995, 5, 18, sep='-', end='!!
')  # GKY-1995-5-18!!

3. Read and write compressed files

import gzip
with open('somefile.gz', 'rt') as f:
    text = f.read()

import bz2
with open('somefile.bz2', 'rt') as f:
    text = f.read()

# Write compressed files
with open('somefile.gz', 'wt') as f:
    f.write(text)

with open('somefile.bz', 'wt') as f:
    f.write(text)