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发表于 2016-8-26 17:36:26
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这是本好书，希望你能坚持下去
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one of the way of of grouping sequence types is by mutability:
Mutable sequences
list , bytearray , array.array , collections.deque and memoryview
Immutable sequences
tuple , str and bytes
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图2-1 主要讲了class collections.abc.Container, class collections.abc.Sized , 和class collections.abc.Iterable 三个抽象类他们是collections.abc 模块下五个抽象类之三，他们是最顶层的抽象类。而class collections.abc.Sequence 继承于Sized, Iterable, Container。MutableSequence 继承于Sequence。当然还有Abstract Methods 和 Mixin Methods 。（可见附图一）
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也就是说那幅图只是能说明inheriting several methods from them），而至于 visualize how mutable sequences differ from immutable ones你就当它扯淡。真正能说明如何区分可变序列和不可变序列的方法，请继续向下阅读。。。
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Immutable sequences
An object of an immutable sequence type cannot change once it is created. (If the object contains references to other objects, these other objects may be mutable and may be changed; however, the collection of objects directly referenced by an immutable object cannot change.)
The following types are immutable sequences:
Strings
A string is a sequence of values that represent Unicode code points. All the code points in the range U+0000 - U+10FFFF can be represented in a string. Python doesn’t have a char type; instead, every code point in the string is represented as a string object with length 1. The built-in function ord() converts a code point from its string form to an integer in the range 0 - 10FFFF; chr() converts an integer in the range 0 - 10FFFF to the corresponding length 1 string object. str.encode() can be used to convert a str to bytes using the given text encoding, and bytes.decode() can be used to achieve the opposite.
Tuples
The items of a tuple are arbitrary Python objects. Tuples of two or more items are formed by comma-separated lists of expressions. A tuple of one item (a ‘singleton’) can be formed by affixing a comma to an expression (an expression by itself does not create a tuple, since parentheses must be usable for grouping of expressions). An empty tuple can be formed by an empty pair of parentheses.
Bytes
A bytes object is an immutable array. The items are 8-bit bytes, represented by integers in the range 0 <= x < 256. Bytes literals (like b'abc') and the built-in function bytes() can be used to construct bytes objects. Also, bytes objects can be decoded to strings via the decode() method.
Mutable sequences
Mutable sequences can be changed after they are created. The subscription and slicing notations can be used as the target of assignment and del (delete) statements.
There are currently two intrinsic mutable sequence types:
Lists
The items of a list are arbitrary Python objects. Lists are formed by placing a comma-separated list of expressions in square brackets. (Note that there are no special cases needed to form lists of length 0 or 1.)
Byte Arrays
A bytearray object is a mutable array. They are created by the built-in bytearray() constructor. Aside from being mutable (and hence unhashable), byte arrays otherwise provide the same interface and functionality as immutable bytes objects.
#### 来自python 3.5.3 documentation
16.9.4 |
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狗仔卡
发表于 2016-8-26 17:36:25
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一定坚持