Python绝技30例

if not sys.version_info > (2, 7):
    # berate your user for running a 10 year 
    # python version
elif not sys.version_info >= (3, 5):
    # Kindly tell your user (s)he needs to upgrade 
    # because you're using 3.5 features

pip3 install ipython

[ expression for item in list if conditional ]

mylist = [i for i in range(10)] 
print(mylist)
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

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

def some_function(a):
    return (a + 5) / 2

my_formula = [some_function(i) for i in range(10)]
print(my_formula)
# [2, 3, 3, 4, 4, 5, 5, 6, 6, 7]

filtered = [i for i in range(20) if i%2==0] 
print(filtered)
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

import sys 2

mylist = range(0, 10000)
print(sys.getsizeof(mylist))
#48

import sys 2
myreallist = [x for x in range(0, 10000)]
print(sys.getsizeof(myreallist))
# 87632

def get_user(id):
    # fetch user from database 
    # ....
    return name, birthdate

name, birthdate = get_user(4)

from dataclasses import dataclass 2

@dataclass
class Card:
    rank: str
    suit: str

card = Card("Q", "hearts") 9

print(card == card)
# True

print(card.rank)
#'Q'

print(card)
Card(rank='Q', suit='hearts')

a=1
b=2
a, b = b, a

print (a)
#2

print (b) 
#1

dict1={'a':1,'b':2}
dict2={'b':3,'c':4}
merged = { **dict1, **dict2 }
print (merged)
# {'a': 1, 'b': 3, 'c': 4}

mystring = "10 awesome python tricks" 
print(mystring.title())
# '10 Awesome Python Tricks'

mystring = "The quick brown fox"
mylist = mystring.split(' ')
print(mylist)
# ['The', 'quick', 'brown', 'fox']

mylist = ['The', 'quick', 'brown', 'fox']
2 mystring = " ".join(mylist)
3 print(mystring)
4 # 'The quick brown fox'

pip3 install emoji

a[start:stop:step]

# 创建一个列表，获取其前两个元素。
first_two = [1, 2, 3, 4, 5][0:2]
print(first_two)
# [1, 2]

# 将步长设置为2，即隔一个取一个元素：
steps = [1, 2, 3, 4, 5][0:5:2]
print(steps)
# [1, 3, 5]

# 字符串也可以做同样的切片。
mystring = "abcdefdn nimt"[::2]
print(mystring)
# 'aced it'

revstring = "abcdefg"[::-1]
print(revstring)
# 'gfedcba'

revarray = [1, 2, 3, 4, 5][::-1]
print(revarray)
# [5, 4, 3, 2, 1]

pip3 install Pillow

from PIL import Image 2
im = Image.open("kittens.jpg")
im.show()
print(im.format, im.size, im.mode)
6 # JPEG (1920, 1357) RGB

map(function, something_iterable)

def upper(s):
    return s.upper()

mylist = list(map(upper, ['sentence', 'fragment']))
print(mylist)
# ['SENTENCE', 'FRAGMENT']

# Convert a string representation of
# a number into a list of ints.
list_of_ints = list(map(int, "1234567")))
print(list_of_ints)
# [1, 2, 3, 4, 5, 6, 7]

mylist=[1,1,2,3,4,5,5,5,6,6]
print (set(mylist))
# {1, 2, 3, 4, 5, 6}

# And since a string can be treated like a
# list of letters, you can also get the
# unique letters from a string this way:
print (set("aaabbbcccdddeeefff"))
# {'a', 'b', 'c', 'd', 'e', 'f'}

test=[1,2,3,4,2,2,3,1,4,4,4] 
print(max(set(test), key = test.count)) 
#4

pip3 install progress

from progress.bar import Bar

bar = Bar('Processing', max=20)
for i in range(20):
    # Do some work
    bar.next() 
bar.finish()

In [1]: 3 * 3 
Out[1]: 9 
In [2]: _ + 3 
Out[2]: 12

python3 -m http.server

s1 = """Multi line strings can be put
        between triple quotes. It's not ideal
        when formatting your code though"""

print(s1)
# Multi line strings can be put
#        between triple quotes. It's not ideal
#        when formatting your code though

s2 = ("You can also concatenate multiple\n" +
        "strings this way, but you'll have to\n"
        "explicitly put in the newlines")

print(s2)
# You can also concatenate multiple
# strings this way, but you'll have to
# explicitly put in the newlines

[on_true] if [expression] else [on_false]

x = "Success!" if (y == 2) else "Failed!"

from collections import Counter

mylist=[1,1,2,3,4,5,5,5,6,6]
c = Counter(mylist)
print(c)
# Counter({1: 2, 2: 1, 3: 1, 4: 1, 5: 3, 6: 2})

# And it works on strings too:
print(Counter("aaaaabbbbbccccc"))
# Counter({'a': 5, 'b': 5, 'c': 5})

x=10 

# Instead of:
if x > 5 and x < 15:
    print("Yes")
#yes

# You can also write:
if 5 < x < 15: 
    print("Yes")
#Yes

from colorama import Fore, Back, Style 2
print(Fore.RED + 'some red text')
print(Back.GREEN + 'and with a green background')
print(Style.DIM + 'and in dim text')
print(Style.RESET_ALL)
print('back to normal now')

pip3 install python-dateutil

from dateutil.parser import parse

logline = 'INFO 2020-01-01T00:00:01 Happy new year, human.'
timestamp = parse(log_line, fuzzy=True)
print(timestamp)
# 2020-01-01 00:00:01

# Python 2 
5 / 2 = 2 
5 / 2.0 = 2.5

#Python 3 
5 / 2 = 2.5 
5 // 2 = 2

pip install chardet

chardetect somefile.txt 
somefile.txt: ascii with confidence 1.0