Python Practice Problems

Python practice problems help beginners to become experts in a python programming language with a small amount of practice effort.

Exit with a status code

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Python Practice › sys Module Programs › Program 3

Exit with a status code

Easysys Module Programs · 3 of 20

Write a Python program that exits with code 1 on failure and show the code the caller sees.

Output
['check.py', 'x'] -> 0 ok
['check.py'] -> 1 missing argument

Approach

  1. sys.exit(1); the parent reads returncode.

Solution

Python
import subprocessimport sys with open("check.py", "w") as f:    f.write("import sys\nif len(sys.argv) < 2:\n    print('missing argument', file=sys.stderr)\n    sys.exit(1)\nprint('ok')\n")for args in [["check.py", "x"], ["check.py"]]:    r = subprocess.run([sys.executable, *args], capture_output=True, text=True)    print(args, "->", r.returncode, (r.stdout or r.stderr).strip())
Output
['check.py', 'x'] -> 0 ok
['check.py'] -> 1 missing argument

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More sys module programs

#4EasyCheck the Python version#5EasyDetect the operating system#6EasyWrite errors to stderr#7EasyRead numbers from stdin

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Read command-line arguments

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Python Practice › sys Module Programs › Program 1

Read command-line arguments

Easysys Module Programs · 1 of 20

Write a Python program that prints its command-line arguments.

Output
show_args.py ['login', '--browser', 'firefox']

Approach

  1. Write a helper script and run it with arguments via subprocess.

Solution

Python
import subprocessimport sys with open("show_args.py", "w") as f:    f.write("import sys\nprint(sys.argv[0], sys.argv[1:])\n")print(subprocess.run([sys.executable, "show_args.py", "login", "--browser", "firefox"],                     capture_output=True, text=True).stdout.strip())
Output
show_args.py ['login', '--browser', 'firefox']

Line by line

Line 5

sys.argv[0] is the script name; the rest are the arguments, as strings.

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#2EasySum numbers from the command line#3EasyExit with a status code#4EasyCheck the Python version#5EasyDetect the operating system

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Palindrome check with deque

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Python Practice › Collections Programs › Program 20

Palindrome check with deque

EasyCollections Programs · 20 of 20

Write a Python program to check palindromes by removing characters from both ends of a deque.

Output
[('Level', True), ('python', False), ('racecar', True)]

Approach

  1. Compare popleft() with pop() until the middle.

Solution

Python
from collections import deque def is_palindrome(word):    d = deque(word.lower())    while len(d) > 1:        if d.popleft() != d.pop():            return False    return True print([(w, is_palindrome(w)) for w in ["Level", "python", "racecar"]])
Output
[('Level', True), ('python', False), ('racecar', True)]

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More collections programs

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Python Collections Programs with Solutions

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Python Practice › Collections Programs

Python Collections Programs with Solutions

20 programs18 easy2 medium0 hard

20 programs for the collections module: Counter for counting, defaultdict for grouping, deque for queues and sliding windows, namedtuple for records, OrderedDict for an LRU cache and ChainMap for layered settings.

Before you start

Read the Collections lesson first if the topic is new to you.

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Invert a dictionary with duplicates

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Python Practice › Collections Programs › Program 19

Invert a dictionary with duplicates

EasyCollections Programs · 19 of 20

Write a Python program to invert a grade dictionary into grade -> students.

Output
{'A': ['asha', 'meena'], 'B': ['ravi'], 'C': ['john']}

Approach

  1. defaultdict(list).

Solution

Python
from collections import defaultdict grades = {"asha": "A", "ravi": "B", "meena": "A", "john": "C"}by_grade = defaultdict(list)for student, grade in grades.items():    by_grade[grade].append(student)print(dict(sorted(by_grade.items())))
Output
{'A': ['asha', 'meena'], 'B': ['ravi'], 'C': ['john']}

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#20EasyPalindrome check with deque

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Top three scorers

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Python Practice › Collections Programs › Program 18

Top three scorers

EasyCollections Programs · 18 of 20

Write a Python program to total player runs from match records and show the top 3.

Output
[('Virat', 143), ('Rohit', 115), ('Gill', 90)]

Approach

  1. Add runs into a Counter.

Solution

Python
from collections import Counter innings = [("Virat", 82), ("Rohit", 45), ("Virat", 61), ("Gill", 90), ("Rohit", 70), ("Rahul", 30)]totals = Counter()for player, runs in innings:    totals[player] += runsprint(totals.most_common(3))
Output
[('Virat', 143), ('Rohit', 115), ('Gill', 90)]

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#19EasyInvert a dictionary with duplicates#20EasyPalindrome check with deque

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Expand a Counter

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Python Practice › Collections Programs › Program 17

Expand a Counter

EasyCollections Programs · 17 of 20

Write a Python program to list every item of a Counter as many times as its count.

Output
['a', 'a', 'b', 'b', 'b', 'c']

Approach

  1. elements().

Solution

Python
from collections import Counterprint(sorted(Counter(a=2, b=3, c=1).elements()))
Output
['a', 'a', 'b', 'b', 'b', 'c']

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#18EasyTop three scorers#19EasyInvert a dictionary with duplicates#20EasyPalindrome check with deque

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Layered settings with ChainMap

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Python Practice › Collections Programs › Program 16

Layered settings with ChainMap

EasyCollections Programs · 16 of 20

Write a Python program that looks up settings in command-line, environment and default layers.

Output
firefox 2 True

Approach

  1. ChainMap(cli, env, defaults) searches left to right.

Solution

Python
from collections import ChainMap defaults = {"browser": "chromium", "retries": 0, "headless": True}env = {"retries": 2}cli = {"browser": "firefox"}settings = ChainMap(cli, env, defaults)print(settings["browser"], settings["retries"], settings["headless"])
Output
firefox 2 True

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More collections programs

#17EasyExpand a Counter#18EasyTop three scorers#19EasyInvert a dictionary with duplicates#20EasyPalindrome check with deque

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namedtuple helpers

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Python Practice › Collections Programs › Program 14

namedtuple helpers

EasyCollections Programs · 14 of 20

Write a Python program using _asdict, _replace and _make.

Output
Point(x=3, y=4) {'x': 3, 'y': 4} Point(x=10, y=4)

Approach

  1. These helpers convert and copy named tuples.

Solution

Python
from collections import namedtuple Point = namedtuple("Point", "x y")p = Point._make([3, 4])print(p, p._asdict(), p._replace(x=10))
Output
Point(x=3, y=4) {'x': 3, 'y': 4} Point(x=10, y=4)

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More collections programs

#15MediumLRU cache with OrderedDict#16EasyLayered settings with ChainMap#17EasyExpand a Counter#18EasyTop three scorers

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LRU cache with OrderedDict

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Python Practice › Collections Programs › Program 15

LRU cache with OrderedDict

MediumCollections Programs · 15 of 20

Write a small least-recently-used cache that holds 2 items.

Output
['a', 'c']

Approach

  1. move_to_end on access; popitem(last=False) evicts the oldest.

Solution

Python
from collections import OrderedDict class LRUCache:    def __init__(self, capacity):        self.capacity = capacity        self.data = OrderedDict()     def get(self, key):        if key not in self.data:            return None        self.data.move_to_end(key)        return self.data[key]     def put(self, key, value):        self.data[key] = value        self.data.move_to_end(key)        if len(self.data) > self.capacity:            self.data.popitem(last=False) cache = LRUCache(2)cache.put("a", 1)cache.put("b", 2)cache.get("a")cache.put("c", 3)print(list(cache.data))
Output
['a', 'c']

Line by line

Lines 22-24

Reading “a” makes it recently used, so adding “c” evicts “b”.

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More collections programs

#16EasyLayered settings with ChainMap#17EasyExpand a Counter#18EasyTop three scorers#19EasyInvert a dictionary with duplicates

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