Python List Problems

Python List Practice Problems

3 × 3 grid

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Python Practice › List Programs › Program 59

3 × 3 grid

EasyList Programs · 59 of 100

Write a Python program to create a 3 × 3 grid where every row is [4, 5, 6].

Output
[[99, 5, 6], [4, 5, 6], [4, 5, 6]]

Approach

  1. Build each row with a comprehension so the rows are separate lists.

Solution

Python
grid = [[4, 5, 6] for _ in range(3)]grid[0][0] = 99print(grid)
Output
[[99, 5, 6], [4, 5, 6], [4, 5, 6]]

Line by line

Line 2

Changing one row proves the rows are independent.

Watch out

[[4, 5, 6]] * 3 repeats the same list object three times, so changing one row would change all of them.

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Pick random numbers from a list

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Python Practice › List Programs › Program 58

Pick random numbers from a list

EasyList Programs · 58 of 100

Write a Python program to select 4 random numbers from a list.

Input
[1, 4, 5, 7, 3, 2, 9]
Output
[3, 5, 2, 1]
9

Approach

  1. random.sample picks without repeats; seed for repeatable output.

Solution

Python
import random random.seed(5)numbers = [1, 4, 5, 7, 3, 2, 9]print(random.sample(numbers, 4))print(random.choice(numbers))
Output
[3, 5, 2, 1]
9

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Insert an item at an index

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Python Practice › List Programs › Program 57

Insert an item at an index

EasyList Programs · 57 of 100

Write a Python program to insert an item at a specific position.

Input
[2, 4, 6, 8, 3, 22], index 3, item 55
Output
[2, 4, 6, 55, 8, 3, 22]

Approach

  1. insert(index, item).

Solution

Python
items = [2, 4, 6, 8, 3, 22]items.insert(3, 55)print(items)
Output
[2, 4, 6, 55, 8, 3, 22]

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More list programs

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Split a list at a given length

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Python Practice › List Programs › Program 56

Split a list at a given length

EasyList Programs · 56 of 100

Write a Python program to split a list into two parts where the first part has a given length.

Input
[4, 6, 7, 3, 2, 5, 6, 7, 6, 4], length 4
Output
[[4, 6, 7, 3], [2, 5, 6, 7, 6, 4]]

Approach

  1. Two slices at the split point.

Solution

Python
items = [4, 6, 7, 3, 2, 5, 6, 7, 6, 4]n = 4print([items[:n], items[n:]])
Output
[[4, 6, 7, 3], [2, 5, 6, 7, 6, 4]]

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Pack consecutive duplicates

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Python Practice › List Programs › Program 55

Pack consecutive duplicates

EasyList Programs · 55 of 100

Write a Python program to pack consecutive duplicates into sublists.

Input
[0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9]
Output
[[0, 0], [1], [2], [3], [4, 4], [5], [6, 6], [7], [8, 8], [9]]

Approach

  1. itertools.groupby groups consecutive equal items.

Solution

Python
from itertools import groupby data = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 7, 8, 8, 9]print([list(group) for _, group in groupby(data)])
Output
[[0, 0], [1], [2], [3], [4, 4], [5], [6, 6], [7], [8, 8], [9]]

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Remove consecutive duplicates

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Python Practice › List Programs › Program 54

Remove consecutive duplicates

EasyList Programs · 54 of 100

Write a Python program to remove consecutive duplicates from a list.

Input
[0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]
Output
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 4]

Approach

  1. Keep an item when it differs from the previous one.

Solution

Python
data = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]result = [x for i, x in enumerate(data) if i == 0 or x != data[i - 1]]print(result)
Output
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 4]

Line by line

Line 2

The first item is always kept; others only when they change.

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Count empty dictionaries

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Python Practice › List Programs › Program 53

Count empty dictionaries

EasyList Programs · 53 of 100

Write a Python program to count the empty dictionaries in a list (ignoring other empty containers).

Input
[{}, {"a": "sqatools"}, [], {}, {"a": 123}, {}, {}, ()]
Output
4

Approach

  1. Count items that are dicts and empty.

Solution

Python
data = [{}, {"a": "sqatools"}, [], {}, {"a": 123}, {}, {}, ()]print(sum(1 for x in data if isinstance(x, dict) and not x))
Output
4
Note

There are 4 empty dicts in this list; the original sample answer said 3.

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Items starting with a letter

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Python Practice › List Programs › Program 52

Items starting with a letter

EasyList Programs · 52 of 100

Write a Python program to find the items that start with a given character.

Input
["abbcd", "ppq", "abdd", "agr", "bhr", "sqqa", "tools", "bgr"]; letters a, b, c
Output
a ['abbcd', 'abdd', 'agr']
b ['bhr', 'bgr']
c []

Approach

  1. Filter with startswith().

Solution

Python
items = ["abbcd", "ppq", "abdd", "agr", "bhr", "sqqa", "tools", "bgr"]for letter in "abc":    print(letter, [w for w in items if w.startswith(letter)])
Output
a ['abbcd', 'abdd', 'agr']
b ['bhr', 'bgr']
c []

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Sublist with the highest sum

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Python Practice › List Programs › Program 51

Sublist with the highest sum

EasyList Programs · 51 of 100

Write a Python program to find the sublist whose elements add up to the highest total.

Input
[[11, 2, 3], [4, 15, 6], [10, 11, 12], [7, 8, 19]]
Output
[7, 8, 19]

Approach

  1. max with key=sum.

Solution

Python
data = [[11, 2, 3], [4, 15, 6], [10, 11, 12], [7, 8, 19]]print(max(data, key=sum))
Output
[7, 8, 19]

Line by line

Line 2

The sums are 16, 25, 33 and 34.

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Move zeros to the end

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Python Practice › List Programs › Program 50

Move zeros to the end

EasyList Programs · 50 of 100

Write a Python program to move all zeros to the end of a list.

Input
[3, 4, 0, 0, 0, 0, 6, 0, 4, 0, 22, 0, 0, 3, 21, 0]
Output
[3, 4, 6, 4, 22, 3, 21, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Approach

  1. Non-zero values followed by the right number of zeros.

Solution

Python
numbers = [3, 4, 0, 0, 0, 0, 6, 0, 4, 0, 22, 0, 0, 3, 21, 0]non_zero = [n for n in numbers if n != 0]print(non_zero + [0] * (len(numbers) - len(non_zero)))
Output
[3, 4, 6, 4, 22, 3, 21, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Line by line

Line 3

[0] * k makes a list of k zeros.

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