住的这个小区也建好几年了，怎么周围一直在装修，钻啊钻啊。于是开大音乐，挡住钻的声音，周期性重复的声音实在是乱人心绪。
边工作边读书，Python Cookbook，将第4章读完了，有的地方实在是太经典，不得不记在博客里，因为不想忘记～
- 代理迭代
构建一个自定义容器对象，包含列表，元组或者其他可迭代对象，定义一个iter()方法，将迭代操作代理到容器内部的对象上。
class Node:
def __init__(self,value):
self._value = value
self._children = []
def __repr__(self):
#使用{!r}和{!s}取得%r和%s的效果
return 'Node({!r})'.format(self._value)
def add_child(self,node):
self._children.append(node)
def __iter__(self):
#返回一个列表的可迭代的对象
return iter(self._children)
if __name__ == "__main__":
root = Node(0)
child1 = Node(1)
child2 = Node(2)
root.add_child(child1)
root.add_child(child2)
for ch in root:
print(ch)```
2. 使用生成器创建迭代模式
def frange(start,stop,increment):
x = start
while x < stop:
yield x
x += increment
def countdown(n):
print("starting to count from ",n)
while n > 0:
yield n
n -= 1
print("done")```
- 关联迭代器类
实现深度优先搜索
别急，后面更精彩……
class Node2:
def __init__(self,value):
self._value = value
self._children = []
def __repr__(self):
return 'Node({!r})'.format(self._value)
def add_child(self,node):
self._children.append(node)
def __iter__(self):
return iter(self._children)
def depth_first(self):
#返回一个该类的实例，该类实现了iter和next方法
return DepthFirstIterator(self)
class DepthFirstIterator(object):
def __init__(self,start_node):
self._node = start_node
self._children_iter = None
self._child_iter = None
def __iter__(self):
return self
def __next__(self):
#第一次next
if self._children_iter is None:
self._children_iter = iter(self._node)
return self._node
elif self._child_iter:
try:
nextchild = next(self._child_iter)
return nextchild
except StopIteration:
self._child_iter = None
return next(self)
else:
self._child_iter = next(self._children_iter).depth_first()
return next(self)```
4. 实现迭代器协议
class Node:
def init(self,value):
self._value = value
self._children = []
def repr(self):
return 'Node({!r})'.format(self._value)
def add_child(self,node):
self._children.append(node)
def iter(self):
return iter(self._children)
def depth_first(self):
yield self
for c in self:
yield from c.depth_first()
if name == "main":
root = Node(0)
child1 = Node(1)
child2 = Node(2)
root.add_child(child1)
root.add_child(child2)
child1.add_child(Node(3))
child2.add_child(Node(4))
child1.add_child(Node(5))
for ch in root.depth_first():
print(ch)```
- reversed()函数返回反向的迭代器
在自定义类上实现__reversed__()方法实现反向迭代
class Countdown:
def __init__(self,start):
self.start = start
def __iter__(self):
n = self.start
while n > 0:
yield n
n -= 1
def __reversed__(self):
n = 1
while n <= self.start:
yield n
n += 1```
6. itertools.islice()方法在迭代器和生成器上做切片操作
def count(n):
while True:
yield n
n += 1
c = count(0)
import itertools
gen = list(itertools.islice(c,10,20))
for x in gen:
print(x)
print(gen,"x",end="")```
- 使用itertools.dropwhile()函数来跳过某些遍历对象
丢弃原有序列中直到函数返回True之前的所有元素
from itertools import dropwhile
with open("/etc/passwd") as f:
for line in dropwhile(lambda line:line.startswith("#"),f):
print(line,end="")```
8. itertools.permutations()遍历集合元素所有可能的排列组合
items = ['a','b','c']
from itertools import permutations
for p in permutations(items):
print(p)```
- enumerate()函数
from collections import defaultdict
#supply missing values
def word(filename):
word_summary = defaultdict(list)
#读取文件行
with open('myfile.txt','r') as f:
lines = f.readlines()
#提取出行与行的序号
for idx,line in enumerate(lines):
words = [w.strip().lower() for w in line.split()]
for word in words:
word_summary[word].append(idx)```
10. zip()同时迭代多个序列
a = [1,2,3]
b = [10,11,12]
c = ['x','y','z']
for i in zip(a,b,c):
print(i)```
- itertools.chain()在不同集合上元素的迭代
from itertools import chain
a = [1,2,3,4]
b = ['x','y','z']
for x in chain(a,b):
print(x)```
12. 多层嵌套的序列展开
yield from在生成器函数中调用其他生成器作为子例程
from collections import Iterable
def flattern(items,ignore_type=(str,bytes)):
for x in items:
if isinstance(x,Iterable) and not isinstance(x,ignore_type):
#use another yield in a yield function
yield from flattern(x)
else:
yield x
items = [1 ,2,[3,4,[5,6],7],8]
for x in flattern(items):
print(x)```
- 顺序序列的合并heapq.merge()
import heapq
a = [1,4,7,10]
b = [2,5,6,11]
for c in heapq.merge(a,b):
print(c)```
14. 迭代来代替while循环
CHUNKSIZE = 8192
def reader(s):
while True:
data = s.recv(CHUNKSIZE)
if data == b'':
break
process_data(data)
这种可以使用iter()代替
iter函数创建一个迭代器,接受callable对象何一个标记
迭代一直到callable对象返回值和标记值相等为止
def reader2(s):
for chunk in iter(lambda: s.recv(CHUNKSIZE),b''):
pass```
- 创建一个类似于shell的数据管道
- fnmatch模块
提供了shell风格的通配符wildcards,like * ? [ seq ] [ !seq ]-
fnmatch.filter(names,pattern)
return the subset of the list of names that match pattern
same as [ n for n in names if fnmatch(n,pattern) ] -
fnmatch.fnmatch(filename,pattern)
test whether the filename string matches the pattern string. -
fnmatch.fnmatchcase(filename,pattern)
the comparison is case-sensitive -
fnmatch.translate(pattern)
return the shell-style pattern converted to a regular expression
-
fnmatch.filter(names,pattern)
- 使用生成器函数来实现管道机制
yield from将yield操作代理到父生成器上
yield from it 返回生成器it所产生的所有值
import os
import fnmatch
import gzip
import bz2
import re
def gen_find(filepat,top):
'''find all filenames and dirs that match a shell wildcards'''
for path,dirlist,filelist in os.walk(top):
for name in fnmatch.filter(filelist,filepat):
#生成路径
yield os.path.join(path,name)
def gen_opener(filenames):
'''open a sequence of filenames producing a file object
and then closed it when proceeding to the next iteration'''
for filename in filenames:
if filename.endswith('.gz'):
f = gzip.open(filename,'rt')
elif filename.endswith('.bz2'):
f = bz2.open(filename,'rt')
else:
f = open(filename,'rt')
#生成文件对象
yield f
f.close()
def gen_concatenate(iterators):
'''chain a sequence of iterators together into a single sequence'''
# for every iterator yielding to generate a sequence
for it in iterators:
#when want to use yield in a yield function, use yield from
yield from it
def gen_grep(pattern,lines):
'''look for a regex pattern in a sequence of lines'''
pat = re.compile(pattern)
for line in lines:
if pat.search(line):
#生成匹配到的line
yield line
#将这些函数连起来创建一个处理管道
lognames = gen_find('access-log*','www')
files = gen_opener(lognames)
lines = gen_concatenate(files)
pylines = gen_grep('python',lines)
for line in pylines:
print(line)```