user_input = "This\nstring has\tsome whitespaces...\r\n"
character_map = {
ord('\n') : ' ',
ord('\t') : ' ',
ord('\r') : None
}
user_input.translate(character_map) # This string has some whitespaces... "unicodedata 库及其 combining() 函数，来生成更大的重映射表（remapping table），并用它来删除字符串中所有的重音。import itertools
s = itertools.islice(range(50), 10, 20) # <itertools.islice object at 0x7f70fab88138>
for val in s:
...itertools.islice，我们可以创建一个 islice 对象，该对象是一个迭代器，可以生成我们所需的内容。但是这有个重要的提醒，即它会消耗掉切片前以及切片对象 islice 中的所有元素。string_from_file = """
// Author: ...
// License: ...
//
// Date: ...
Actual content...
"""
import itertools
for line in itertools.dropwhile(lambda line:line.startswith("//"), string_from_file.split("\n")):
print(line)def test(*, a, b):
pass
test("value for a", "value for b") # TypeError: test() takes 0 positional arguments...
test(a="value", b="value 2") # Works...class Connection:
def __init__(self):
...
def __enter__(self):
# Initialize connection...
def __exit__(self, type, value, traceback):
# Close connection...
with Connection() as c:
# __enter__() executes
...
# conn.__exit__() executesfrom contextlib import contextmanager
@contextmanager
def tag(name):
print(f"<{name}>")
yield
print(f"</{name}>")
with tag("h1"):
print("This is Title.")class Person:
__slots__ = ["first_name", "last_name", "phone"]
def __init__(self, first_name, last_name, phone):
self.first_name = first_name
self.last_name = last_name
self.phone = phoneimport signal
import resource
import os
# To Limit CPU time
def time_exceeded(signo, frame):
print("CPU exceeded...")
raise SystemExit(1)
def set_max_runtime(seconds):
# Install the signal handler and set a resource limit
soft, hard = resource.getrlimit(resource.RLIMIT_CPU)
resource.setrlimit(resource.RLIMIT_CPU, (seconds, hard))
signal.signal(signal.SIGXCPU, time_exceeded)
# To limit memory usage
def set_max_memory(size):
soft, hard = resource.getrlimit(resource.RLIMIT_AS)
resource.setrlimit(resource.RLIMIT_AS, (size, hard))setrlimit 和获取的硬限制对其进行设置。def foo():
pass
def bar():
pass
__all__ = ["bar"]from some_module import * 在使用时可以导入的内容。对于以上示例，通配导入时只会导入 bar。此外，我们可以将__all__ 设为空，令其无法导出任何东西，并且在使用通配符方式从此模块中导入时，将引发 AttributeError。functools.total_ordering 可救场：from functools import total_ordering
@total_ordering
class Number:
def __init__(self, value):
self.value = value
def __lt__(self, other):
return self.value < other.value
def __eq__(self, other):
return self.value == other.value
print(Number(20) > Number(3))
print(Number(1) < Number(5))
print(Number(15) >= Number(15))
print(Number(10) <= Number(2))# ID First Name Last Name
line_record = "2 John Smith"
ID = slice(0, 8)
FIRST_NAME = slice(9, 21)
LAST_NAME = slice(22, 27)
name = f"{line_record[FIRST_NAME].strip()} {line_record[LAST_NAME].strip()}"
# name == "John Smith"import getpass
user = getpass.getuser()
password = getpass.getpass()
# Do Stuff...import difflib
difflib.get_close_matches('appel', ['ape', 'apple', 'peach', 'puppy'], n=2)
# returns ['apple', 'ape']import ipaddress
net = ipaddress.ip_network('74.125.227.0/29') # Works for IPv6 too
# IPv4Network('74.125.227.0/29')
for addr in net:
print(addr)
# 74.125.227.0
# 74.125.227.1
# 74.125.227.2
# 74.125.227.3
# ...ip = ipaddress.ip_address("74.125.227.3")
ip in net
# True
ip = ipaddress.ip_address("74.125.227.12")
ip in net
# Falsepython3.8 -i 运行你的程序——一旦你的程序终止了， -i 会启动交互式 shell，在那你可以查看所有的变量和调用函数。整洁，但是使用实际的调试器（pdb ）会如何呢？让我们用以下程序（script.py ）：def func():
return 0 / 0
func()python3.8 -i script.py运行脚本：# Script crashes...
Traceback (most recent call last):
File "script.py", line 4, in <module>
func()
File "script.py", line 2, in func
return 0 / 0
ZeroDivisionError: division by zero
>>> import pdb
>>> pdb.pm() # Post-mortem debugger
> script.py(2)func()
-> return 0 / 0
(Pdb)def func():
breakpoint() # import pdb; pdb.set_trace()
return 0 / 0
func()script.py(3)func()
-> return 0 / 0
(Pdb) # we start here
(Pdb) step
ZeroDivisionError: division by zero
> script.py(3)func()
-> return 0 / 0
(Pdb)import datetime
class Date:
def __init__(self, year, month, day):
self.year = year
self.month = month
self.day = day
@classmethod
def today(cls):
t = datetime.datetime.now()
return cls(t.year, t.month, t.day)
d = Date.today()
print(f"{d.day}/{d.month}/{d.year}")
# 14/9/2019*args 、**kwargs 和一堆 if 语句，而不是使用类方法来解决。那可能行得通，但是却变得难以阅读和维护。lru_cache :from functools import lru_cache
import requests
@lru_cache(maxsize=32)
def get_with_cache(url):
try:
r = requests.get(url)
return r.text
except:
return "Not Found"
for url in ["https://google.com/",
"https://martinheinz.dev/",
"https://reddit.com/",
"https://google.com/",
"https://dev.to/martinheinz",
"https://google.com/"]:
get_with_cache(url)
print(get_with_cache.cache_info())
# CacheInfo(hits=2, misses=4, maxsize=32, currsize=4)from collections import Counter
cheese = ["gouda", "brie", "feta", "cream cheese", "feta", "cheddar",
"parmesan", "parmesan", "cheddar", "mozzarella", "cheddar", "gouda",
"parmesan", "camembert", "emmental", "camembert", "parmesan"]
cheese_count = Counter(cheese)
print(cheese_count.most_common(3))
# Prints: [('parmesan', 4), ('cheddar', 3), ('gouda', 2)]print(cheese_count["mozzarella"])
# Prints: 1
cheese_count["mozzarella"] += 1
print(cheese_count["mozzarella"])
# Prints: 2