Python中一些不为人知的基础技巧总结

# bad
if image.endswith('.jpg') or image.endswith('.png') or image.endswith('.gif'):
 pass
# good
if image.endswith(('.jpg', '.png', '.gif')):
 pass
# bad
if url.startswith('http:') or url.startswith('https:') or url.startswith('ftp:'):
 pass
# good
if url.startswith(('http:', 'https:', 'ftp:')):
 pass

# bad
for index, v in enumerate(data):
 print(index+1, v)
# good
for index, v in enumerate(data, start=1):
 print(index, v)

record = '....................100.................513.25......'
# bad
cost = int(record[20:23]) * float(record[40:46])
# good
SHARES = slice(20, 23)
PRICE = slice(40, 46)
cost = int(record[SHARES]) * float(record[PRICE])

>>> items = [0, 1, 2, 3, 4, 5, 6]
>>> a = slice(2, 4)
>>> items[2:4]
[2, 3]
>>> items[a]
[2, 3]
>>> items[a] = [-2, -3]
>>> items
[0, 1, -2, -3, 4, 5, 6]
>>> del items[a]
>>> items
[0, 1, 4, 5, 6]
>>>

 with open('input.txt', 'r') as source:
 with open('output.txt', 'w') as target:
  target.write(source.read())

 with open('input.txt', 'r') as source, open('output.txt', 'w') as target:
  target.write(source.read())

>>> for i in range(3):
...  print(i)
... else:
...  print('Iterated over everything')
... 
0
1
2
Iterated over everything
>>>

>>> for i in range(3):
...  if i == 2:
...   break
...  print(i)
... else:
...  print('Iterated over everything')
... 
0
1
>>>

try：
 dangerous_call()
 after_call()
except OSError:
 log('OSError...')

try:
 dangerous_call()
except OSError:
 log('OSError...')
else:
 after_call()