Скачать или смотреть Python MCQ 113 - dict, Test Your Skills

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Python MCQ Questions and answers,
Python MCQ , Python Programming,
Python, Python Type,
dict, dictionary type, key-value pair
Python dictionary, Python dict
dictionaries, python dictionaries

Dict(key-value pair) unpacking:
**dict→only within other dicts or
function call as Keyword arguments
print(**d)⇒TypeError
→if d is not print's valid kargs
x=**a, or x,**y = a⇒SyntaxError

Iterable unpacking:
*itr
→works anywhere
Refer MCQs 77 to 82
→In function call as
Positional arguments
Note: *dict⇒only keys

p = {a: b}
⇒dict literal syntax {}.
→It uses values of variables a, b as the key: value
⇒{6: 8}.
q = dict(a=b)
⇒dict() constructor with keyword argument.
→ a is string literal key, name of the keyword argument with its value is variable b's value.
⇒{'a': 8}

dict operation,
d.items()
⇒ tuples structure: (key,value)
Membership test
(k,v) in d.items() or
(k,v) not in d.items()
(k,v) in d.items()⇔ k in d and d[k] == v
Check a key:
k in d⇔k in d.keys()
⇒ True if d has key k,
else False.
k not in d
Check a value:
v in d.values()

In dict, Only keys→ unique,
value→duplicates
→The fundamental rule.
→During creation or updates, enforces unique keys, where duplicate keys overwrites existing values ensuring each key maps to exactly one value.

dict operation,
setdefault,
setdefault(key, default=None)
If key is in the dictionary, return its value. If not, insert key with a value of default and return default. default defaults to None.
d.setdefault(k, dv)
default value dv→optional, if ignored→uses None.
if key k is in d
⇒return its value, irrespective of dv.
else
⇒inserts k with dv, returns dv
(dv→either specified or None)

Comparing dict.values() to itself, will always return False.

Comparison of d.keys(), d.items() implemented to be based on the contents like set operations not identity.

Use list(d.values) to compare dict values.
list(d.values()) == list(d.values())⇒True
Since values can be mutable, unhashable, and may contain duplicates.
Since keys, items are unique and hashable.

dict creation
→Empty
1) {}⇔dict()
→Values
2) comma-separated list of
key: value pairs within {}
Also called mapping.
3) dict(**kwargs)
keys→valid identifiers
4) dict(mapping, /, **kwargs)
5) dict(iterable, /, **kwargs)
Each item in iterable must
be an iterable with exactly
two itms.
6) dict comprehension
{x: x ** 2 for x in range(5)}

Features:
1. Comma-separated list of key:value pairs within braces {}.
2. Mutable object that preserve insertion order.
3. Keys must be hashable (immutable).
4. Keys allow mixed data type.
5. Values allow duplicates
6. Values can be of any data type.

Dictionary
Set of key: value pairs with unique keys.
If a key occurs more than once, the last value overwrites any previous value.
Hashable: int, float, str, tuple with immutable items, frozenset
Unhashable: list, set, dict

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#ssitlecturestamil ‎@ssitlecturestamilதமிழ் 

*a→positional args
**b→keyword args
*a unpacks ['Tom','Jey'] →'Tom','Jey'
**b unpacks {'sep': ' and ','end': '!!!'}→sep=' and ', end='!!!'
⇒print('Tom', 'Jey',sep=' and ', end='!!!')
⇒Tom and Jey!!!

By default, dict d iterate over keys.
Dict d:
1) print(d), repr(d)
⇒treat d as a string representation
of d as key: value pairs.

2) Other operations
⇒treat d as an iterator over keys unless using d.values(), d.items() explicitly.
⇒so d or d.keys() is same.
Ex: for k in d:, list(d), *d,
k in d, len(d)


Key: Value pairs must be unique
2) →Incorrect
→Pair Uniqueness Misconception
→May mislead as the rule itself does not define the pair as the unique constraint.

1) Both keys and values must be unique
4) Only values must be unique
⇒1), 4)→Incorrect
→Values can be duplicated
→Same value can appear more than once for different key.

dict→Not supports integer
based indexing or slicing
d[k]
⇒if key k exists in d
returns its value
else raises KeyError


d.get(k, default)
⇒if key k exists in d
returns its value
else default
⇒No KeyError
default
→optional
→any user-defined information
→not given⇒returns None