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a.md

name: inverse layout: true class: center, middle, inverse

Python 简介

su27

layout: false .left-column[

What is Python?

] .right-column[

Python: 优雅而健壮的编程语言

  • 高级

  • 易学易读易维护

  • 兼顾解释性和编译性的优点

  • 面向对象

  • 一些函数化编程的结构

  • 高效快速，扩展库众多 ]

.left-column[

What is Python?

] .right-column[

  • 动态语言

    .python

    a = 1 a = 'asdf'

  • 强类型语言

    .python

    a = '1' a + 2 Traceback (most recent call last): File "", line 1, in TypeError: cannot concatenate 'str' and 'int' objects

  • 一切皆对象

    • 变量名只是一个名字，它指向一个对象

    • 赋值操作其实是绑定操作

      .python

      (1).class int ]

.left-column[

交互式环境

]

.right-column[

  • python

  • ipython

  • help()

  • docstring

    .python

    help(list)

    Help on class list in module builtin:

    class list(object) | list() -> new empty list | list(iterable) -> new list initialized from iterable's items | | Methods defined here: | | add(...) | x.add(y) <==> x+y | | contains(...) | x.contains(y) <==> y in x | ]

.left-column[

Data Structures

] .right-column[

数值

  • int: 100 , 0x3e

  • long

    • 并不是C或者其他编译类型语言的长整型

    .python

    import sys

    sys.maxint 9223372036854775807

    sys.maxint+1 9223372036854775808L

    999999 ** 9 999991000035999916000125999874000083999964000008999999L

  • float: 1.1

  • complex: (9+3j) ]

.left-column[

Data Structures

]

.right-column[

数值运算

  • 除法

    .python

    5 / 2 2 5.0 / 2 2.5 from future import division 5 / 2 2.5

  • 其他运算 ]

.left-column[

Data Structures

]

.right-column[

String

  • 字符串是不可变的

  • 字符串的切片和成员操作

    .python

    s = 'hello douban' s[1:5] 'ello' s[:5] 'hello' s[-6:] 'douban'

    'dou' in s True 'yah' in s False ]

.left-column[

Data Structures

]

.right-column[

String

  • 字符串的连接与格式化

    .python

    print '哈' * 5 哈哈哈哈哈

    '' + 'button' + '' 'button'

    '%s' % ('red', 'button') 'button'

    '{2}-{0}-{1}'.format('1', '4', '2013') '2013-1-4'

    coord = (3, 5) 'X: {0[0]}; Y: {0[1]}'.format(coord) 'X: 3; Y: 5'

    coord = {'latitude': '37.24N', 'longitude': '-115.81W'} 'Target: {latitude}, {longitude}'.format(**coord) 'Target: 37.24N, -115.81W' ]

.left-column[

Data Structures

]

.right-column[

String

  • 字符串的连接与格式化

    .python

    #不好:

    s = '' for i in seq: s += chr(i)

    #好:

    ''.join(chr(i) for i in seq) ]

.left-column[

Data Structures

]

.right-column[

String

  • str:

  • 'douban.com'

  • '\xe8\xb1\x86\xe7\x93\xa3'

  • unicode

  • u'\u8c46\u74e3'

  • 转换

    .python

    '豆瓣' '\xe8\xb1\x86\xe7\x93\xa3'

    '豆瓣'.decode('utf8') u'\u8c46\u74e3'

    u'\u8c46\u74e3'.encode('utf8') '\xe8\xb1\x86\xe7\x93\xa3'

]

.left-column[

Data Structures

]

.right-column[

字符串的方法

find, index, rfind, rindex, count

startswith, endswith, isalpha, isdigit, isalnum, islower, isupper, isspace

encode, decode, lower, upper, strip, lstrip, rstrip, replace

split, rsplit, splitlines

join

]

.left-column[

Data Structures

]

.right-column[

容器

tuple: (1000001, 'ahbei') , (1,)

list: [1, 2, 3, 4, 5]

dict: {'CEO': 'ahbei', 'Team Members': ['brant', 'hongqn', ...]}

set: set([1, 2, 3])

]

.left-column[

Data Structures

]

.right-column[

list

  • 切片

  • append , insert , pop, remove, reverse , sort

  • index , count (没有find)

  • 使用 list 模拟栈操作

    .python

    stack = [3, 4, 5] stack.append(6) stack.append(7) stack [3, 4, 5, 6, 7] stack.pop() 7

  • 使用list.insert模拟队列不如 collections.deque

    .python

    from collections import deque queue = deque(["Eric", "John", "Michael"]) queue.append("Terry") # Terry arrives queue.popleft() # The first to arrive now leaves 'Eric' ]

.left-column[

Data Structures

] .right-column[

FP tools for list

filter

.python
>>> def f(x): return x % 2 != 0 and x % 3 != 0
>>> filter(f, range(2, 25))
[5, 7, 11, 13, 17, 19, 23]

map

.python
>>> seq = range(8)
>>> def add(x, y): return x+y
>>> map(add, seq, seq)
[0, 2, 4, 6, 8, 10, 12, 14]

]

.left-column[

Data Structures

] .right-column[

列表解析

A.

>>> squares = []
>>> for x in range(10):
...     squares.append(x ** 2)
>>> squares
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

B.

>>> squares = map(lambda x: x ** 2, range(10))

C. (list Comprehension)

>>> squares = [x ** 2 for x in range(10)]

]

.left-column[

Data Structures

] .right-column[

列表解析: 多变量及过滤条件

exam A: flatten a list

>>> vec = [[1,2,3], [4,5,6], [7,8,9]]
>>> [num for elem in vec for num in elem]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

exam B:

>>> combs = []
>>> for x in [1,2,3]:
...     for y in [3,1,4]:
...         if x != y:
...             combs.append((x, y))
>>> combs
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

# equals to:
>>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]

]

.left-column[

Data Structures

] .right-column[

dict

.python
>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
>>> dict(sape=4139, guido=4127, jack=4098)
{'sape': 4139, 'jack': 4098, 'guido': 4127}

# Dict Comprehensions
>>> {x: x ** 2 for x in (2, 4, 6)}
{2: 4, 4: 16, 6: 36}

  • set: d['name'] = 'Jim', update, setdefault

  • delete: del d['CEO'], pop, popitem, clear

  • get: get, has_key (deprecated), keys, values, items

  • iter: iterkeys, itervalues, iteritems

  • copy, deepcopy

    .python

    Kid = {'h': '165', 'like': {'laptop': 'mac', 'book': []}} Kim = Kid.copy() Kim['like']['book'].append('LOTR') Kid['like'] {'laptop': 'mac', 'book': ['LOTR']} ]

.left-column[

Data Structures

] .right-column[

set

set的修改:

add, discard, remove, clear, copy, update

set的运算:

union(|), difference(-), intersection(*), symmetric_difference(^)

子集的判断:

issubset, issuperset, &gt;, &lt; ]

.left-column[

Data Structures

] .right-column[

tuple

  • 元组是不可变类型

    .python

    不可赋值

    t = (1, 2) t[0] += 1 Traceback (most recent call last): File "", line 1, in TypeError: 'tuple' object does not support item assignment

    可做dict的key

    d = {} d[['a']] = 1 Traceback (most recent call last): File "", line 1, in TypeError: unhashable type: 'list' d[(1,2)] = 1

  • mutable: list, dict, set, 类实例

  • immutable: 数值类型, 字符串, tuple

]

.left-column[

Data Structures

] .right-column[

tuple

  • 某种程度的可变

    .python

    d = (1, ['A', 'B']) d[1].append('C') d (1, ['A', 'B', 'C'])

  • 单元素元组

    .python

    type((1)) <type 'int'> type((1,)) <type 'tuple'>

    word = 'hello', len(word) 1 word ('hello',) ]

.left-column[

Data Structures

] .right-column[

tuple

  • Unpacking

    result, = (1024,) result 1024

    a, b = b, a ]

.left-column[

Data Structures

] .right-column[

collections

Specialized container datatypes, providing alternatives to Python’s general purpose built-in containers, dict, list, set, and tuple.

Counter

.python
>>> c = Counter(a=4, b=2, c=0, d=-2)
>>> d = Counter(a=1, b=2, c=3, d=4)
>>> list(c.elements())
['a', 'a', 'a', 'a', 'b', 'b']
>>> c.subtract(d)
>>> c
Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})

# An example:
>>> words = re.findall(r'\w+', open('hamlet.txt').read().lower())
>>> Counter(words).most_common(10)
[('the', 1143), ('and', 966), ('to', 762), ('of', 669), ('i', 631),
 ('you', 554),  ('a', 546), ('my', 514), ('hamlet', 471), ('in', 451)]

]

.left-column[

Data Structures

] .right-column[

collections

  • OrderedDict

    .python

    d = OrderedDict([('first', 1), ... ('second', 2), ... ('third', 3)]) d.items() [('first', 1), ('second', 2), ('third', 3)]

  • deque

  • defaultdict

  • namedtuple

]

.left-column[

Control Flow Tools

] .right-column[

分支

  • if...elif...else
  • 悬挂问题

C:

.c
if (x > 0)
    if (y > 0)
        printf('x,y available!\n');
else
    printf('not available!\n');

python:

.python
if x > 0:
    if y > 0:
        print 'x,y available!'
else:
    print 'not available!'

]

.left-column[

Control Flow Tools

] .right-column[

分支

  • 条件判断与 bool()

    .python toys = [] if len(toys) == 0: # 或者 if toys != [] print "boring..."

    better

    if not toys: print "boring..."

  • 三元操作 x if condition else y

    .python answer = 'yeah' if toys else 'no'

]

.left-column[

Control Flow Tools

] .right-column[

循环

  • while

  • for i in ...:

  • while和for都可以有else

    .python def find_cat(cat, boxes): for box in boxes: if box.is_empty: continue elif cat in box: print "The cat is in", box break else: print "We have lost the cat."

其他

  • break, continue, pass, ... ]

.left-column[

Control Flow Tools

] .right-column[

循环

  • Example A

    .python

    不好

    for i in range(len(seq)): foo(seq[i], i)

    好:

    for i, item in enumerate(seq): foo(item, i)

  • Example B

    #不好: for i in xrange(len(seq1)): foo(seq1[i], seq2[i])

    #好: for i, j in zip(seq1, seq2): foo(i, j)

    for i, j in itertools.izip(seq1, seq2): foo(i, j) ]

.left-column[

Control Flow Tools

] .right-column[

异常

  • 所有异常都是Exception的子类

    • 除了KeyboardInterrupted和SystemExit
    • ValueError, KeyError, etc...

    .python try: do_something() except KeyError: handle_key_error() except Exception, e: import traceback traceback.print_exc() finally: release_resources()

  • raise ]

.left-column[

Control Flow Tools

] .right-column[

异常

  • 不要做这样的事情

    .python try: do_something() except: pass ]

.left-column[

Modules

] .right-column[

A module is a file containing Python definitions and statements.

.python
# fibo.py
author = 'su27'
_author_age = 27
def fib(n): # write Fibonacci series up to n
    a, b = 0, 1
    while b < n:
        print b,
        a, b = b, a+b

  • import modules to use

    .python

    import fibo fibo.fib(1000) 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 fibo.author 'su27' fibo.name 'fibo' ]

.left-column[

Modules

] .right-column[

名称空间与作用域

Local, Global, 与 Built-ins 名称空间

自由区隔的名字空间

.python
def foo():
    pass
foo.__doc__ = '呀，刚才忘了加上doc字符串'
foo.version = 0.2

import即是把名字导入当前的名称空间

]

.left-column[

Modules

] .right-column[

import的方式

.python
>>> import fibo
>>> from fibo import fib, author

>>> from fibo import * # 绝大多数情况下要避免这样用
>>> author
'su27'
>>> _author_age
Traceback (most recent call last):
  File or: name '_author_age' is not defined

Note: import的时候, 被import的模块代码将被执行

]

.left-column[

Iterators

] .right-column[

迭代器

  • 迭代器用起来是什么感觉？

    .python for element in [1, 2, 3]: print element for key in {'one':1, 'two':2}: print key for key, value in {'one':1, 'two':2}.items(): print key, value for char in "123": print char for line in open("myfile.txt"): print line

  • xrange和range

  • iterkeys, iteritems

]

.left-column[

Iterators

] .right-column[

迭代器

  • for在这里做了什么?

    .python

    s = 'abc' it = iter(s) it <iterator object at 0x00A1DB50> it.next() 'a' it.next() 'b' it.next() 'c' it.next() Traceback (most recent call last): File "", line 1, in ? it.next() StopIteration ]

.left-column[

Iterators

] .right-column[

迭代器

  • 能被迭代的是这样的对象: 把它传给iter(), 运行后会返回一个支持next()方法的对象

  • 写一个:

    .python class Reverse: """Iterator for looping over a sequence backwards.""" def init(self, data): self.data = data self.index = len(data) def iter(self): return self def next(self): if self.index == 0: raise StopIteration self.index = self.index - 1 return self.data [self.index]

    rev = Reverse('spam') iter(rev) <main.Reverse object at 0x00A1DB50> for char in rev: ... print char ]

.left-column[

Iterators

Generators

] .right-column[

生成器

  • 生成器是一种简单强大的创建迭代器的方法, 用yield代替return， 这样每次被调用next的时候，就会一直执行到下一次yield.

    .python def reverse(data): for index in range(len(data)-1, -1, -1): yield data[index]

    for char in reverse('red'): ... print char d e r

  • BTW...

    .python for char in reversed(data): yield char

    for char in data[::-1]: yield char ]

.left-column[

Iterators

Generators

Generator Expressions

] .right-column[

生成器表达式

  • 把列表解析的方括号换成圆括号

    .python

    sum(x * y for x,y in zip(xvec, yvec)) # dot product 260

    page = ('this is a big dog', 'this is a small cat')

    List comprehension to set

    words = set([word for line in page for word in line.split()])

    Set comprehension

    words = {word for line in page for word in line.split()}

    Generator expression to set

    words = set(word for line in page for word in line.split())

    words set(['a', 'this', 'big', 'is', 'dog', 'cat', 'small'])

]

.left-column[

Functions

] .right-column[

python中的函数

.python
def foo(value):
    return value, value % 2

关键字参数和默认参数

.python
def net_conn(host, port=80):
    print "connect to %s:%s" % (host, port)

>>> net_conn('douban', 8080)
>>> net_conn(port=8080, host='douban')

默认参数要在关键字参数前面

]

.left-column[

Functions

] .right-column[

哪些调用是错的？

, port=80): print "connect to %s://%s:%s" % (scheme, host, port)

>>> net_conn('http', 'douban', host='8080')

>>> net_conn('douban', scheme='http', port=8080)

>>> net_conn(port=8080, host='douban', 'http')

>>> net_conn(port=8080, host='douban', scheme='http')

>>> net_conn(scheme='http', 'douban', port='8080')

>>> net_conn('http', port='8080')

>>> net_conn('http', 'douban')

>>> net_conn('http', 'douban', 8080, 'tcp')

]

.left-column[

Functions

] .right-column[

哪些调用是错的？

.python
def net_conn(scheme, host='douban', port=80):
    print "connect to %s://%s:%s" % (scheme, host, port)

>>> net_conn('http', 'douban', host='8080')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: net_conn() got multiple values for keyword argument 'host'

>>> net_conn('douban', scheme='http', port=8080)
  File "<stdin>", line 1
TypeError: net_conn() got multiple values for keyword argument 'scheme'

>>> net_conn(port=8080, host='douban', 'http')
  File "<stdin>", line 1
SyntaxError: non-keyword arg after keyword arg

>>> net_conn(port=8080, host='douban', scheme='http')
connect to http://douban:8080

]

.left-column[

Functions

] .right-column[

哪些调用是错的？

.python
def net_conn(scheme, host='douban', port=80):
    print "connect to %s://%s:%s" % (scheme, host, port)

>>> net_conn(scheme='http', 'douban', port='8080')
  File "<stdin>", line 1
SyntaxError: non-keyword arg after keyword arg

>>> net_conn('http', port='8080')
connect to http://douban:8080

>>> net_conn('http', 'douban')
connect to http://douban:80

>>> net_conn('http', 'douban', 8080, 'tcp')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: net_conn() takes at most 3 arguments (4 given)

]

.left-column[

Functions

] .right-column[

可变长度的参数

  • 用一个元组接受可变长默认参数

    .python def func(arg1, arg2, *rest): print 'arg1:', arg1 print 'arg2:', arg2 for arg in rest: print 'extra arg:', arg

  • 用一个字典接受可变长关键字参数

    .python def func(arg1, arg2, **rest): print 'arg1:', arg1 print 'arg2:', arg2 for arg in rest: print 'extra arg: %s=%s' % (arg, rest[arg])

]

.left-column[

Functions

] .right-column[

可变长度的参数

.python
>>> def f(x, *args, **kwargs):
...     print 'x:', x, 'args:', args, 'kwargs:', kwargs
...
>>> f(1)
x: 1 args: () kwargs: {}

>>> f(1, 2, 3)
x: 1 args: (2, 3) kwargs: {}

>>> f(1, 2, n=3)
x: 1 args: (2,) kwargs: {'n': 3}

]

.left-column[

Functions

] .right-column[

匿名函数与lambda

  • lambda [arg1[, arg2, ..., argN]]: expression

    .python

    sorted([('Bo', 24), ('Yi', 23), ('Si', 31)], key=lambda p: p[1]) [('Yi', 23), ('Bo', 24), ('Si', 31)]

    map((lambda x: x+' me'), ['love', 'hate', 'kill']) ['love me', 'hate me', 'kill me']

    reduce((lambda x,y: x+y), range(10)) 45 ] def net_conn(scheme, host='douban'"", line 1, in NameErr

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