1、 Exchange two numbers in place
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x, y =10, 20
print(x, y)
y, x = x, y
print(x, y)
10 20
20 10
2、 Chain comparison operators
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n = 10
print(1 < n < 20)
print(1 > n <= 9)
True
False
3、 Use ternary operators to implement conditional assignment
[ The expression returns the true value ] if [ expression ] else [ The expression is a false return value ]
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y = 20
x = 9 if (y == 10) else 8
print(x)
8
# look for abc The smallest number in
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def small(a, b, c):
return a if a<b and a<c else (b if b<a and b<c else c)
print(small(1, 0, 1))
print(small(1, 2, 2))
print(small(2, 2, 3))
print(small(5, 4, 3))
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# The list of deduction
x = [m**2 if m>10 else m**4 for m in range(50)]
print(x)
[0, 1, 16, 81, 256, 625, 1296, 2401, 4096, 6561, 10000, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625, 676, 729, 784, 841, 900, 961, 1024, 1089, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1764, 1849, 1936, 2025, 2116, 2209, 2304, 2401]
4、 Multiline string
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multistr = "select * from multi_row \
where row_id < 5"
print(multistr)
select * from multi_row where row_id < 5
multistr = """select * from multi_row
where row_id < 5"""
print(multistr)
select * from multi_row
where row_id < 5
multistr = ("select * from multi_row"
"where row_id < 5"
"order by age")
print(multistr)
select * from multi_rowwhere row_id < 5order by age
5、 Store list elements into new variables
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testList = [1, 2, 3]
x, y, z = testList # The number of variables should be strictly consistent with the length of the list
print(x, y, z)
1 2 3
6、 Print the absolute path of the incoming module
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import threading
import socket
print(threading)
print(socket)
<module 'threading' from 'd:\\python351\\lib\\threading.py'>
<module 'socket' from 'd:\\python351\\lib\\socket.py'>
7、 Interactive environment “_” The operator
stay python Console , Whether we test an expression or call a method , The results are assigned to a temporary variable “_”
8、 Dictionaries / Set inference
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testDic = {i: i * i for i in range(10)}
testSet = {i * 2 for i in range(10)}
print(testDic)
print(testSet)
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}
{0, 2, 4, 6, 8, 10, 12, 14, 16, 18}
9、 Debug script
use pdb Module set breakpoint
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import pdb
pdb.ste_trace()
10、 Turn on file sharing
python Allow to open a HTTP The server shares files from the root directory
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python -m http.server
11、 Check python Objects in the
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test = [1, 3, 5, 7]
print(dir(test))
['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
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test = range(10)
print(dir(test))
['__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'count', 'index', 'start', 'step', 'stop']
12、 simplify if sentence
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# use following way to verify multi values
if m in [1, 2, 3, 4]:
# do not use following way
if m==1 or m==2 or m==3 or m==4:
13、 Runtime detection python edition
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import sys
if not hasattr(sys, "hexversion") or sys.version_info != (2, 7):
print("sorry, you are not running on python 2.7")
print("current python version:", sys.version)
sorry, you are not running on python 2.7
current python version: 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:54:25) [MSC v.1900 64 bit (AMD64)]
14、 Combine multiple strings
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test = ["I", "Like", "Python"]
print(test)
print("".join(test))
['I', 'Like', 'Python']
ILikePython
15、 Four kinds of flipped strings 、 The way of listing
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1
16、 Use enumeration to find the index in the loop
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test = [10, 20, 30]
for i, value in enumerate(test):
print(i, ':', value)
0 : 10
1 : 20
2 : 30
17、 Define enumerators
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class shapes:
circle, square, triangle, quadrangle = range(4)
print(shapes.circle)
print(shapes.square)
print(shapes.triangle)
print(shapes.quadrangle)
0
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18、 Returns multiple values from a method
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def x():
return 1, 2, 3, 4
a, b, c, d = x()
print(a, b, c, d)
1 2 3 4
19、 Use * Operator unpack Function parameter
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def test(x, y, z):
print(x, y, z)
testDic = { 'x':1, 'y':2, 'z':3}
testList = [10, 20, 30]
test(*testDic)
test(**testDic)
test(*testList)
z x y
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10 20 30
20、 Use a dictionary to store expressions
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stdcalc = {
"sum": lambda x, y: x + y,
"subtract": lambda x, y: x - y
}
print(stdcalc["sum"](9, 3))
print(stdcalc["subtract"](9, 3))
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21、 Calculate the factorial of any number
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import functools
result = (lambda k: functools.reduce(int.__mul__, range(1, k+1), 1))(3)
print(result)
6
22、 Find the number that appears most frequently in the list
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test = [1, 2, 3, 4, 2, 2, 3, 1, 4, 4, 4, 4]
print(max(set(test), key=test.count))
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23、 Reset recursion limit
python Limit the number of recursions to 1000, You can reset
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import sys
x = 1200
print(sys.getrecursionlimit())
sys.setrecursionlimit(x)
print(sys.getrecursionlimit())
1000
1200
24、 Check the memory usage of an object
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import sys
x = 1
print(sys.getsizeof(x)) # python3.5 In a 32 Bit integer occupancy 28 byte
28
25、 Use slots Reduce memory costs
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import sys
# Original class
class FileSystem(object):
def __init__(self, files, folders, devices):
self.files = files
self.folder = folders
self.devices = devices
print(sys.getsizeof(FileSystem))
# After reducing memory
class FileSystem(object):
__slots__ = ['files', 'folders', 'devices']
def __init__(self, files, folders, devices):
self.files = files
self.folder = folders
self.devices = devices
print(sys.getsizeof(FileSystem))
1016
888
26、 use lambda To mimic the output method
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import sys
lprint = lambda *args: sys.stdout.write(" ".join(map(str, args)))
lprint("python", "tips", 1000, 1001)
python tips 1000 1001
27、 Build a dictionary from two related sequences
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t1 = (1, 2, 3)
t2 = (10, 20, 30)
print(dict(zip(t1, t2)))
{1: 10, 2: 20, 3: 30}
28、 Multiple prefixes of the search string
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print("http://localhost:8888/notebooks/Untitled6.ipynb".startswith(("http://", "https://")))
print("http://localhost:8888/notebooks/Untitled6.ipynb".endswith((".ipynb", ".py")))
True
True
29、 Construct a list without a loop
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import itertools
import numpy as np
test = [[-1, -2], [30, 40], [25, 35]]
print(list(itertools.chain.from_iterable(test)))
[-1, -2, 30, 40, 25, 35]
30、 Realization switch-case sentence
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def xswitch(x):
return xswitch._system_dict.get(x, None)
xswitch._system_dict = { "files":10, "folders":5, "devices":2}
print(xswitch("default"))
print(xswitch("devices"))
None
