1、原地交換兩個數字
1
2
3
4
x, y
=
10
,
20
print
(x, y)
y, x
=
x, y
print
(x, y)
10 20
20 10
2、鏈狀比較操作符
1
2
3
n
=
10
print
(
1
< n <
20
)
print
(
1
> n <
=
9
)
True
False
3、使用三元操作符來實現條件賦值
[表達式為真的返回值] if [表達式] else [表達式為假的返回值]
1
2
3
y
=
20
x
=
9
if
(y
=
=
10
)
else
8
print
(x)
8
# 找abc中最小的數
1
2
3
4
5
6
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
))
0
1
3
3
1
2
3
# 列表推導
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、多行字符串
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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、存儲列表元素到新的變量
1
2
3
testList
=
[
1
,
2
,
3
]
x, y, z
=
testList
# 變量個數應該和列表長度嚴格一致
print
(x, y, z)
1 2 3
6、打印引入模塊的絕對路徑
1
2
3
4
5
6
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、交互環境下的“_”操作符
在python控制台,不論我們測試一個表達式還是調用一個方法,結果都會分配給一個臨時變量“_”
8、字典/集合推導
1
2
3
4
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、調試腳本
用pdb模塊設置斷點
1
2
import
pdb
pdb.ste_trace()
10、開啟文件分享
python允許開啟一個HTTP服務器從根目錄共享文件
1
python
-
m http.server
11、檢查python中的對象
1
2
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']
1
2
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、簡化if語句
1
2
3
4
# 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、運行時檢測python版本
1
2
3
4
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、組合多個字符串
1
2
3
test
=
[
"I"
,
"Like"
,
"Python"
]
print
(test)
print
("".join(test))
['I', 'Like', 'Python']
ILikePython
15、四種翻轉字符串、列表的方式
5
3
1
16、用枚舉在循環中找到索引
1
2
3
test
=
[
10
,
20
,
30
]
for
i, value
in
enumerate
(test):
print
(i,
':'
, value)
0 : 10
1 : 20
2 : 30
17、定義枚舉量
1
2
3
4
5
6
class
shapes:
circle, square, triangle, quadrangle
=
range
(
4
)
print
(shapes.circle)
print
(shapes.square)
print
(shapes.triangle)
print
(shapes.quadrangle)
0
1
2
3
18、從方法中返回多個值
1
2
3
4
def
x():
return
1
,
2
,
3
,
4
a, b, c, d
=
x()
print
(a, b, c, d)
1 2 3 4
19、使用*運算符unpack函數參數
1
2
3
4
5
6
7
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
1 2 3
10 20 30
20、用字典來存儲表達式
1
2
3
4
5
6
stdcalc
=
{
"sum"
:
lambda
x, y: x
+
y,
"subtract"
:
lambda
x, y: x
-
y
}
print
(stdcalc[
"sum"
](
9
,
3
))
print
(stdcalc[
"subtract"
](
9
,
3
))
12
6
21、計算任何數的階乘
1
2
3
import
functools
result
=
(
lambda
k: functools.
reduce
(
int
.__mul__,
range
(
1
, k
+
1
),
1
))(
3
)
print
(result)
6
22、找到列表中出現次數最多的數
1
2
test
=
[
1
,
2
,
3
,
4
,
2
,
2
,
3
,
1
,
4
,
4
,
4
,
4
]
print
(
max
(
set
(test), key
=
test.count))
4
23、重置遞歸限制
python限制遞歸次數到1000,可以用下面方法重置
1
2
3
4
5
import
sys
x
=
1200
print
(sys.getrecursionlimit())
sys.setrecursionlimit(x)
print
(sys.getrecursionlimit())
1000
1200
24、檢查一個對象的內存使用
1
2
3
import
sys
x
=
1
print
(sys.getsizeof(x))
# python3.5中一個32比特的整數占用28字節
28
25、使用slots減少內存開支
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
import
sys
# 原始類
class
FileSystem(
object
):
def
__init__(
self
, files, folders, devices):
self
.files
=
files
self
.folder
=
folders
self
.devices
=
devices
print
(sys.getsizeof(FileSystem))
# 減少內存後
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、用lambda 來模仿輸出方法
1
2
3
import
sys
lprint
=
lambda
*
args: sys.stdout.write(
" "
.join(
map
(
str
, args)))
lprint(
"python"
,
"tips"
,
1000
,
1001
)
python tips 1000 1001
27、從兩個相關序列構建一個字典
1
2
3
t1
=
(
1
,
2
,
3
)
t2
=
(
10
,
20
,
30
)
print
(
dict
(
zip
(t1, t2)))
{1: 10, 2: 20, 3: 30}
28、搜索字符串的多個前後綴
1
2
print
(
"http://localhost:8888/notebooks/Untitled6.ipynb"
.startswith((
"http://"
,
"https://"
)))
print
(
"http://localhost:8888/notebooks/Untitled6.ipynb"
.endswith((
".ipynb"
,
".py"
)))
True
True
29、不使用循環構造一個列表
1
2
3
4
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、實現switch-case語句
1
2
3
4
5
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