Python 库大全（下）！知道的都是大佬！（附代码讲解）

>>> import reprlib
>>> reprlib.repr(set(\'supercalifragilisticexpialidocious\'))
"{\'a\', \'c\', \'d\', \'e\', \'f\', \'g\', ...}"

>>> import pprint
>>> t = [[[[\'black\', \'cyan\'], \'white\', [\'green\', \'red\']], [[\'magenta\',
...     \'yellow\'], \'blue\']]]
...
>>> pprint.pprint(t, width=30)
[[[[\'black\', \'cyan\'],
   \'white\',
   [\'green\', \'red\']],
  [[\'magenta\', \'yellow\'],
   \'blue\']]]

>>> import textwrap
>>> doc = """The wrap() method is just like fill() except that it returns
... a list of strings instead of one big string with newlines to separate
... the wrapped lines."""
...
>>> print(textwrap.fill(doc, width=40))
The wrap() method is just like fill()
except that it returns a list of strings
instead of one big string with newlines
to separate the wrapped lines.

>>> import locale
>>> locale.setlocale(locale.LC_ALL, \'English_United States.1252\')
\'English_United States.1252\'
>>> conv = locale.localeconv()          # 获取一种惯例的映射
>>> x = 1234567.8
>>> locale.format("%d", x, grouping=True)
\'1,234,567\'
>>> locale.format_string("%s%.*f", (conv[\'currency_symbol\'],
...                      conv[\'frac_digits\'], x), grouping=True)
\'$1,234,567.80\'

>>> from string import Template
>>> t = Template(\'${village}folk send $$10 to $cause.\')
>>> t.substitute(village=\'Nottingham\', cause=\'the ditch fund\')
\'Nottinghamfolk send $10 to the ditch fund.\'

>>> t = Template(\'Return the $item to $owner.\')
>>> d = dict(item=\'unladen swallow\')
>>> t.substitute(d)
Traceback (most recent call last):
  ...
KeyError: \'owner\'
>>> t.safe_substitute(d)
\'Return the unladen swallow to $owner.\'

>>> import time, os.path
>>> photofiles = [\'img_1074.jpg\', \'img_1076.jpg\', \'img_1077.jpg\']
>>> class BatchRename(Template):
...     delimiter = \'%\'
>>> fmt = input(\'Enter rename style (%d-date %n-seqnum %f-format):  \')
Enter rename style (%d-date %n-seqnum %f-format):  Ashley_%n%f

>>> t = BatchRename(fmt)
>>> date = time.strftime(\'%d%b%y\')
>>> for i, filename in enumerate(photofiles):
...     base, ext = os.path.splitext(filename)
...     newname = t.substitute(d=date, n=i, f=ext)
...     print(\'{0} --> {1}\'.format(filename, newname))

img_1074.jpg --> Ashley_0.jpg
img_1076.jpg --> Ashley_1.jpg
img_1077.jpg --> Ashley_2.jpg

import struct

with open(\'myfile.zip\', \'rb\') as f:
    data = f.read()

start = 0
for i in range(3):                      # 显示前三行的头文件
    start += 14
    fields = struct.unpack(\'<IIIHH\', data[start:start+16])
    crc32, comp_size, uncomp_size, filenamesize, extra_size = fields

    start += 16
    filename = data[start:start+filenamesize]
    start += filenamesize
    extra = data[start:start+extra_size]
    print(filename, hex(crc32), comp_size, uncomp_size)

    start += extra_size + comp_size     # 跳过下一个头文件

import threading, zipfile

class AsyncZip(threading.Thread):
    def __init__(self, infile, outfile):
        threading.Thread.__init__(self)
        self.infile = infile
        self.outfile = outfile

    def run(self):
        f = zipfile.ZipFile(self.outfile, \'w\', zipfile.ZIP_DEFLATED)
        f.write(self.infile)
        f.close()
        print(\'后台解压文件完成:\', self.infile)

background = AsyncZip(\'mydata.txt\', \'myarchive.zip\')
background.start()
print(\'主程序持续执行.\')

background.join()    # 等待后台任务完成
print(\'主程序等待后台任务结束.\')

import logging
logging.debug(\'Debugging information\')
logging.info(\'Informational message\')
logging.warning(\'Warning:config file %s not found\', \'server.conf\')
logging.error(\'Error occurred\')
logging.critical(\'Critical error -- shutting down\')

WARNING:root:Warning:config file server.conf not found
ERROR:root:Error occurred
CRITICAL:root:Critical error -- shutting down

>>> import weakref, gc
>>> class A:
...     def __init__(self, value):
...         self.value = value
...     def __repr__(self):
...         return str(self.value)
...
>>> a = A(10)                   # 创建一个应用
>>> d = weakref.WeakValueDictionary()
>>> d[\'primary\'] = a            
>>> d[\'primary\']                # 如果对象仍然是活动的，则获取它
10
>>> del a                       # 删除一个引用
>>> gc.collect()                # 立即运行垃圾收集
0
>>> d[\'primary\']                # 条目被自动删除
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    d[\'primary\']                # 条目被自动删除
  File "C:/python37/lib/weakref.py", line 46, in __getitem__
    o = self.data[key]()
KeyError: \'primary\'

>>> from array import array
>>> a = array(\'H\', [4000, 10, 700, 22222])
>>> sum(a)
26932
>>> a[1:3]
array(\'H\', [10, 700])

>>> from collections import deque
>>> d = deque(["task1", "task2", "task3"])
>>> d.append("task4")
>>> print("Handling", d.popleft())
Handling task1

unsearched = deque([starting_node])
def breadth_first_search(unsearched):
    node = unsearched.popleft()
    for m in gen_moves(node):
        if is_goal(m):
            return m
        unsearched.append(m)

>>> import bisect
>>> scores = [(100, \'perl\'), (200, \'tcl\'), (400, \'lua\'), (500, \'python\')]
>>> bisect.insort(scores, (300, \'ruby\'))
>>> scores
[(100, \'perl\'), (200, \'tcl\'), (300, \'ruby\'), (400, \'lua\'), (500, \'python\')]

>>> from heapq import heapify, heappop, heappush
>>> data = [1, 3, 5, 7, 9, 2, 4, 6, 8, 0]
>>> heapify(data)                      # 将列表重新排列为堆顺序
>>> heappush(data, -5)                 # 添加一个新项
>>> [heappop(data) for i in range(3)]  # 获取三个最小的项
[-5, 0, 1]

>>> from decimal import *
>>> round(Decimal(\'0.70\') * Decimal(\'1.05\'), 2)
Decimal(\'0.74\')
>>> round(.70 * 1.05, 2)
0.73

>>> Decimal(\'1.00\') % Decimal(\'.10\')
Decimal(\'0.00\')
>>> 1.00 % 0.10
0.09999999999999995

>>> sum([Decimal(\'0.1\')]*10) == Decimal(\'1.0\')
True
>>> sum([0.1]*10) == 1.0
False

>>> getcontext().prec = 36
>>> Decimal(1) / Decimal(7)
Decimal(\'0.142857142857142857142857142857142857\')