python data structure note

Python筆記整理(Python 3.4)

Reference

Python tutorial

https://docs.python.org/3/tutorial/index.html

http://www.swaroopch.com/notes/python/

http://www.codedata.com.tw/python/python-tutorial-the-2nd-class-2-container-flow-for-comprehension/

運算子

>>> 17 / 3 # classic division returns a float ,單斜線浮點數 5.666666666666667

>>> 17 // 3 # floor division discards the fractional part,雙斜線浮點數整數 5

>>> 17 % 3 # the % operator returns the remainder of the division, 百分比餘數 2

>>> 5 ** 2 # 5 squared,雙星號平方 25

>>> tax = 12.5 / 100 >>> price = 100.50 >>> price * tax 12.5625 >>> price + _ # 變數_,可以用來表示最後的運算結果 113.0625

>>> a = 5 >>> a += 1 # 連加不使用++, 而是+= >>> a 6

字串string

字串可以用單引號或是雙引號來表示,反斜線用來保護要印出的引號

>>> 'spam eggs' # single quotes 'spam eggs' >>> "doesn't" # ...or use double quotes instead "doesn't" >>> "\"Yes,\" he said." '"Yes," he said.'

加r來避免固定字

>>> print('C:\some\name') # here \n means newline! C:\some ame >>> print(r'C:\some\name') # note the r before the quote C:\some\name

印出多行可使用"""...""" or '''…'''

print("""\ Usage: thingy [OPTIONS] -h Display this usage message -H hostname Hostname to connect to """)

字串可以用加號來連接,用星號來複製

>>> 3 * 'un' + 'ium' 'unununium'

字串陣列引數可以有正負號

+---+---+---+---+---+---+ | P | y | t | h | o | n | +---+---+---+---+---+---+ 0 1 2 3 4 5 6 -6 -5 -4 -3 -2 -1 >>> word[:2] # character from the beginning to position 2 (excluded) 'Py' >>> word[-2:] # characters from the second-last (included) to the end 'on'

陣列裡的數值無法被改變(immutable)

>>> word[0] = 'J' ... TypeError: 'str' object does not support item assignment

可以用len()來偵測字串長度

>>> s = 'supercalifragilisticexpialidocious' >>> len(s) 34

串列List(mutable),與string享有共同操作

跟字元陣列一樣有正負號的引數,也可以用加號連接,用星號來複製,用len來偵測長度

不一樣的是他的數值可以被改變

>>> cubes = [1, 8, 27, 65, 125] # something's wrong here >>> 4 ** 3 # the cube of 4 is 64, not 65! 64 >>> cubes[3] = 64 # replace the wrong value >>> cubes [1, 8, 27, 64, 125]

可以形成二維

>>> a = ['a', 'b', 'c'] >>> n = [1, 2, 3] >>> x = [a, n] >>> x [['a', 'b', 'c'], [1, 2, 3]] >>> x[0] ['a', 'b', 'c'] >>> x[0][1] 'b'

list還有下列函式可以使用

>>> a = [1,4,2,6] >>> a.append(3) # 增加數值 >>> a [1, 4, 2, 6, 3] >>> a.remove(4) # 移除數值 >>> a [1, 2, 6, 3] >>> a.pop() # 移除最後一位的數值 3 >>> a [1, 2, 6] >>> a.sort() # 排序 >>> a [1, 2, 6] >>> a.reverse() # 順序顛倒 >>> a [6, 2, 1] >>> >>> a.index(1) # 列出數值6的index 2 >>> del a[0] # 移除引數0 >>> a [2, 1] >>>

List 也可以當作queues來用

>>> from collections import deque >>> queue = deque(["Eric", "John", "Michael"]) >>> queue.append("Terry") # Terry arrives >>> queue.append("Graham") # Graham arrives >>> queue.popleft() # The first to arrive now leaves 'Eric' >>> queue.popleft() # The second to arrive now leaves 'John' >>> queue # Remaining queue in order of arrival deque(['Michael', 'Terry', 'Graham'])

list還有更多的延伸功能,可以看一下這裡https://docs.python.org/3/tutorial/datastructures.html

5.1.1-5.1.4

Range()

代表由0開始到i-1

>>> for i in range(5): ... print(i) ... 0 1 2 3 4

如果range裡面有三個變數,最後一個表示間隔

range(5, 10) 5 through 9 range(0, 10, 3) 0, 3, 6, 9 range(-10, -100, -30) -10, -40, -70

Tuple (immutable)

tuple內的數值是不可被改變的,可以用分號或是括號來表示

>>> t = 123,456,'hihi' >>> t[1] 456 >>> t[1] = 123 Traceback (most recent call last): File "<pyshell#2>", line 1, in <module> t[1] = 123 TypeError: 'tuple' object does not support item assignment >>> t (123, 456, 'hihi') >>>

因為tuple是不可變動的,所以要對tuple做變動的話,要先將其轉成list

>>> t = 2,5,4,8,6 >>> t (2, 5, 4, 8, 6) >>> t.sort() Traceback (most recent call last): File "<pyshell#14>", line 1, in <module> t.sort() AttributeError: 'tuple' object has no attribute 'sort' >>> t1 = list(t) >>> t1.sort() >>> t1 [2, 4, 5, 6, 8] >>>

其他更多有關tuple的資訊可以看這http://openhome.cc/Gossip/Python/TupleType.html

Sets無序群集

其牽涉到物件相等性(hashable),要建立一個set必須用{}

An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() or __cmp__() method). Hashable objects which compare equal must have the same hash value.

Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.

>>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'} >>> print(basket) # show that duplicates have been removed {'orange', 'banana', 'pear', 'apple'} >>> 'orange' in basket # fast membership testing True >>> 'crabgrass' in basket False >>> # Demonstrate set operations on unique letters from two words ... >>> a = set('abracadabra') >>> b = set('alacazam') >>> a # unique letters in a {'a', 'r', 'b', 'c', 'd'} >>> a - b # letters in a but not in b {'r', 'd', 'b'} >>> a | b # letters in either a or b {'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'} >>> a & b # letters in both a and b {'a', 'c'} >>> a ^ b # letters in a or b but not both {'r', 'd', 'b', 'm', 'z', 'l'}

Dict

其是將key與value對應的物件,也是hashable,可用list(d.keys())或sorted(d.keys())

>>> tel = {'jack': 4098, 'sape': 4139} >>> tel['guido'] = 4127 >>> tel {'sape': 4139, 'guido': 4127, 'jack': 4098} >>> tel['jack'] 4098 >>> del tel['sape'] >>> tel['irv'] = 4127 >>> tel {'guido': 4127, 'irv': 4127, 'jack': 4098} >>> list(tel.keys()) ['irv', 'guido', 'jack'] >>> sorted(tel.keys()) ['guido', 'irv', 'jack'] >>> 'guido' in tel True >>> 'jack' not in tel False

其他更多有關set與dict的範例可以看這5.6

https://docs.python.org/3/tutorial/datastructures.html

因為python有這麼方便的list與tuple,使用者可以更方便的操控資料型態,把時間用在刀口上!!!!