Python Practice Problems

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

Initialise with default values

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Python Practice › Dictionary Programs › Program 87

Initialise with default values

EasyDictionary Programs · 87 of 94

Write a Python program to give every name its own copy of a default settings dictionary.

Input
["Virat", "Rohit"], {"sport": "cricket", "salary": 100000}
Output
{'Virat': {'sport': 'cricket', 'salary': 100000}, 'Rohit': {'sport': 'cricket', 'salary': 120000}}

Approach

  1. Copy the defaults for each name.

Solution

Python
names = ["Virat", "Rohit"]defaults = {"sport": "cricket", "salary": 100000}players = {name: defaults.copy() for name in names}players["Rohit"]["salary"] = 120000print(players)
Output
{'Virat': {'sport': 'cricket', 'salary': 100000}, 'Rohit': {'sport': 'cricket', 'salary': 120000}}

Line by line

Line 3

.copy() gives each player an independent dict, so changing Rohit’s salary does not change Virat’s.

Watch out

dict.fromkeys(names, defaults) would share one dict between all names.

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List of all values

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Python Practice › Dictionary Programs › Program 86

List of all values

EasyDictionary Programs · 86 of 94

Write a Python program to get a list of all values.

Input
{"sqa": 1, "tools": 2, "is": 2, "best": 4}
Output
[1, 2, 2, 4]

Approach

  1. list(d.values()).

Solution

Python
print(list({"sqa": 1, "tools": 2, "is": 2, "best": 4}.values()))
Output
[1, 2, 2, 4]

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More dictionary programs

#87EasyInitialise with default values#88EasyDelete several keys#89EasyRename a key#90EasyInvert a dictionary with repeated values

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List of all keys

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Python Practice › Dictionary Programs › Program 85

List of all keys

EasyDictionary Programs · 85 of 94

Write a Python program to get a list of all keys.

Input
{"sqa": [1, 2, 5, 6], "tools": [3, 8, 9], "is": [2, 5, 0], "best": [3, 6, 8]}
Output
['sqa', 'tools', 'is', 'best']

Approach

  1. list(d).

Solution

Python
print(list({"sqa": [1, 2, 5, 6], "tools": [3, 8, 9], "is": [2, 5, 0], "best": [3, 6, 8]}))
Output
['sqa', 'tools', 'is', 'best']

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More dictionary programs

#86EasyList of all values#87EasyInitialise with default values#88EasyDelete several keys#89EasyRename a key

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Dictionary to a list of tuples

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Python Practice › Dictionary Programs › Program 84

Dictionary to a list of tuples

EasyDictionary Programs · 84 of 94

Write a Python program to convert a dictionary to a list of (key, value) tuples.

Input
{"a": 19, "b": 20, "c": 21, "d": 20}
Output
[('a', 19), ('b', 20), ('c', 21), ('d', 20)]

Approach

  1. list(d.items()).

Solution

Python
print(list({"a": 19, "b": 20, "c": 21, "d": 20}.items()))
Output
[('a', 19), ('b', 20), ('c', 21), ('d', 20)]

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More dictionary programs

#85EasyList of all keys#86EasyList of all values#87EasyInitialise with default values#88EasyDelete several keys

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Keys with a given value

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Python Practice › Dictionary Programs › Program 83

Keys with a given value

EasyDictionary Programs · 83 of 94

Write a Python program to find all keys that have a given value.

Input
{"a": 19, "b": 20, "c": 21, "d": 20}, value 20
Output
['b', 'd']

Approach

  1. Filter items().

Solution

Python
d = {"a": 19, "b": 20, "c": 21, "d": 20}print([k for k, v in d.items() if v == 20])
Output
['b', 'd']

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More dictionary programs

#84EasyDictionary to a list of tuples#85EasyList of all keys#86EasyList of all values#87EasyInitialise with default values

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Values of one key from many dicts

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Python Practice › Dictionary Programs › Program 82

Values of one key from many dicts

EasyDictionary Programs · 82 of 94

Write a Python program to get the values of a key from a list of dictionaries.

Input
[{"name": "jos", "age": 30}, {"name": "david", "age": 25}, {"name": "virat", "age": 32}], key "age"
Output
[30, 25, 32]

Approach

  1. A comprehension.

Solution

Python
data = [{"name": "jos", "age": 30}, {"name": "david", "age": 25}, {"name": "virat", "age": 32}]print([d["age"] for d in data])
Output
[30, 25, 32]

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More dictionary programs

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Which keys contain each value

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Python Practice › Dictionary Programs › Program 81

Which keys contain each value

EasyDictionary Programs · 81 of 94

Write a Python program to show, for each value, the keys whose lists contain it.

Input
{"xyz": [20, 40], "abc": [10, 20]}
Output
{20: ['xyz', 'abc'], 40: ['xyz'], 10: ['abc']}

Approach

  1. Invert into defaultdict(list).

Solution

Python
from collections import defaultdict d = {"xyz": [20, 40], "abc": [10, 20]}inverted = defaultdict(list)for key, values in d.items():    for v in values:        inverted[v].append(key)print(dict(inverted))
Output
{20: ['xyz', 'abc'], 40: ['xyz'], 10: ['abc']}

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More dictionary programs

#82EasyValues of one key from many dicts#83EasyKeys with a given value#84EasyDictionary to a list of tuples#85EasyList of all keys

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Unique values from list values

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Python Practice › Dictionary Programs › Program 80

Unique values from list values

EasyDictionary Programs · 80 of 94

Write a Python program to extract the unique values from all list values, sorted.

Input
{"sqa": [1, 2, 5, 6], "tools": [3, 8, 9], "is": [2, 5, 0], "best": [3, 6, 8]}
Output
[0, 1, 2, 3, 5, 6, 8, 9]

Approach

  1. A set comprehension, then sort.

Solution

Python
d = {"sqa": [1, 2, 5, 6], "tools": [3, 8, 9], "is": [2, 5, 0], "best": [3, 6, 8]}print(sorted({x for v in d.values() for x in v}))
Output
[0, 1, 2, 3, 5, 6, 8, 9]

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More dictionary programs

#81EasyWhich keys contain each value#82EasyValues of one key from many dicts#83EasyKeys with a given value#84EasyDictionary to a list of tuples

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Dictionary with the most keys

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Python Practice › Dictionary Programs › Program 79

Dictionary with the most keys

EasyDictionary Programs · 79 of 94

Write a Python program to find which of two dictionaries has more keys.

Input
{"name": 1, "age": 2}, {"name": 1, "age": 2, "course": 3, "institute": 4}
Output
2nd dictionary has maximum keys, 4

Approach

  1. Compare len().

Solution

Python
a = {"name": 1, "age": 2}b = {"name": 1, "age": 2, "course": 3, "institute": 4}bigger = max([("1st", a), ("2nd", b)], key=lambda p: len(p[1]))print(f"{bigger[0]} dictionary has maximum keys, {len(bigger[1])}")
Output
2nd dictionary has maximum keys, 4

Learn the concept

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More dictionary programs

#80EasyUnique values from list values#81EasyWhich keys contain each value#82EasyValues of one key from many dicts#83EasyKeys with a given value

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Value at a nested path

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Python Practice › Dictionary Programs › Program 78

Value at a nested path

MediumDictionary Programs · 78 of 94

Write a Python program to get the value at a path of keys and indexes in nested data.

Input
{"p1": {"name": {"first": "lionel", "last": "messi"}, "team": ["psg", "argentina"]}}
Output
Messi
Argentina

Approach

  1. Follow the path one step at a time with functools.reduce.

Solution

Python
from functools import reduce data = {"p1": {"name": {"first": "lionel", "last": "messi"}, "team": ["psg", "argentina"]}} def get_path(obj, path):    return reduce(lambda acc, key: acc[key], path, obj) print(get_path(data, ["p1", "name", "last"]).title())print(get_path(data, ["p1", "team", 1]).title())
Output
Messi
Argentina

Line by line

Lines 5-6

reduce applies acc[key] for each key in turn, starting from the whole object; indexes work for lists.

Learn the concept

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More dictionary programs

#79EasyDictionary with the most keys#80EasyUnique values from list values#81EasyWhich keys contain each value#82EasyValues of one key from many dicts

← All 94 Dictionary Programs