Lec15-Mutability

2024-10-17 197 words One minute

Contents

Mutability

date

Obj in Python

String

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s = "Hello"
s.swapcase() # "hELLO"

ASCII

和表格对应 0x41 –> row 4, col 1 😮

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from unicodedata import name, lookup
name('A') # 'LATIN CAPITAL LETTER A'
lookup('LATIN CAPITAL LETTER A') # 'A'
lookup('SNOWMAN') # '☃'
lookup('FACE WITH TEARS OF JOY').encode('utf-8') # '😂'.encode('utf-8')

Mutation operations

Mutable objects

List
Dictionary
Set?

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# List, pop, remove, append, extend
lst = [1, 2, 3]
lst.pop() # 3
lst.remove(2) # [1]
lst.append(4) # [1, 4]
lst.extend([5, 6]) # [1, 4, 5, 6]

赋值的时候，如果是可变对象，则会影响到原对象，如果是不可变对象，则会创建新的对象。 😮

Immutable objects

Tuple
String
Number

Immutable objects are hashable, which means that they can be used as keys in dictionaries and as elements in sets.

An immutable object can be changed if it contains a mutable object.

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s = ([1, 2], 4)
s[0][0] = 8 # correct
s[0] = 5 # incorrect

Mutation

same or change?

Identity: a is b is in Python
Equality: a == b == in Python

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def f(s=[]):
    s.append(1)
    return s

f() # [1]
f() # [1, 1]
f() # [1, 1, 1]

frame里面引用传递更加常见 🤔