Python 開發中高階技巧

>>> chars = [ c for c in

'python']
>>>chars['
p', '
y', '
t', '
h', '
o', '
n']

>>> dict1 = 

>>> double_dict1 = 
>>>double_dict1

>>> set1 = 

>>> double_set = 
>>>double_set

>>> x = 

>>> y = 
>>> z = 
>>>z

>>> nums = [1,2,3]

>>>nums[::]
[1, 2, 3]
>>> copy_nums =nums[::]
>>>copy_nums
[1, 2, 3]

>>> reverse_nums = nums[::-1]

>>>reverse_nums
[3, 2, 1]

>>> a,b = 1, 2

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

>>> a, *b = 1,2,3

>>>a
1>>>b
[2, 3]

或者

>>> a, *b, c = 1,2,3,4,5
>>>a
1>>>b
[2, 3, 4]
>>>c
5

>>> def

f():
...     
return 1, 2, 3, 4...
>>> a, b, c, d =f()
>>>a
1>>>d
4

>>> "

".join(["
i", "
love
", "
python"])
'i love python
'

>>> if a > 2 and a < 5:

...     
pass
...>>> if 2:
...     
pass

#

沒有使用 field from
defdup(n):
for i in
range(n):
yield
i        
yieldi#
使用yield from
defdup(n):
for i in
range(n):
yield
from
[i, i]
for i in dup(3):
print
(i)>>>001
122

>>> if x == 1 or x == 2 or x == 3:

...     
pass
...>>> if x in (1,2,3):
...     
pass

def

fun(x):
if x == 'a'
:        
return 1
elif x == 'b'
:        
return 2
else
:        
return
none
deffun(x):
return .get(x)

>>> for i, e in enumerate(["

a","
b","c"
]):...     
print
(i, e)
...0 a
1b2 c

注意區分列表推導式，生成器效率更高

>>> g = (i**2 for i in range(5))
>>>g
at 0x10881e518>
>>> for i in
g:...     
print
(i)...01
4916

>>> d =dict()

>>> d['
nums']
keyerror: 
'nums
'>>>
>>> from collections import
defaultdict
>>> d =defaultdict(list)
>>> d["
nums"]

>>> lang = '

python
'>>> f'
is most popular language in the world''
python is most popular language in the world
'

>>> nums = [1,2,3,3]

>>> max(set(nums), key=nums.count)
3或者from collections import
counter
>>>counter(nums).most_common()[0][0]
3

>>> with open("

test.txt
", "w"
) as f:
...     f.writelines(
"hello
")

>>>isinstance(a, (int, str))

true
類似的還有字串的 startswith，endswith
前者對人友好，可讀性更強，後者對計算機友好，支援 obj == eval(repr(obj))
def

makebold(f):
return
lambda: "

" + f() + "
"
defmakeitalic(f):
return
lambda: "
" + f() + "
"@makebold
@makeitalic
defsay():
return
"hello
">>>say()
hello不使用裝飾器，可讀性非常差
defsay():
return
"hello
">>>makebold(makeitalic(say))()
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