1. 遍历输出数组
array = ['a', 'b', 'c', 'd']
# The bad way
i = 0
for arr in array:
print i, arr
i += 1
# The better way
for i, arr in enumerate(array):
print i, arr
# Run and output
>>>
0 a
1 b
2 c
3 d
0 a
1 b
2 c
3 d
2. 交叉遍历两个数组
x_list = [1, 2, 3]
y_list = [4, 5, 6]
# The bad way
for i in range(len(x_list)):
x = x_list[i]
y = y_list[i]
print x, y
# The better way
for x, y in zip(x_list, y_list):
print x, y
# Run and output
>>>
1 4
2 5
3 6
1 4
2 5
3 6
3. 交换两个变量的值
x = 1
y = 2
print x, y
# The bad way
temp = y
y = x
x = temp
print x, y
x = 1
y = 2
print x, y
# The better way
x, y = y, x
print x, y
# Run and output
>>>
1 2
2 1
1 2
2 1
4. Dict 用 get 取某个 key 值
dic = {
'Name' :'John',
'City' :'Shanghai'
}
# The bad way
city = ''
if dic.has_key('City'):
city = dic['City']
else:
city = 'Unknown'
print city
# The better way
city = dic.get('City', 'Unknown')
print city
# Test the no-key condition
dic = {
'Name' :'John',
'Sex' :'Male'
}
city = dic.get('City', 'Unknown')
print city
# Run and output
>>>
Shanghai
Shanghai
Unknown
5. 利用 for 循环的 else
find = 'b'
array = ['b', 'b', 'c', 'd', 'e']
# The bad way
found = False
for arr in array:
if find == arr:
print 'Found!'
found = True
break
if not found:
print 'Not found!'
# The better way
for arr in array:
if find == arr:
print 'Found!'
break
else: # This else means no-break occurred
print 'Not found!'
# Test the not-found condition
find = 'f'
for arr in array:
if find == arr:
print 'Found!'
break
else: # This else means no-break occurred
print 'Not found!'
# Run and output
>>>
Found!
Found!
Not found!
6. 读取文件
# The bad way
f = open('xxx.txt')
text = f.read()
for line in text.split('\n'):
print line
f.close()
# The better way
with open('xxx.txt') as f:
for line in f:
print line
7. 异常的 else
print 'Converting...'
print int('1')
print 'Done'
# The bad way
print 'Converting...'
try:
print int('x')
except:
print 'Conversion failed.'
print 'Done'
# The better way
print 'Converting...'
try:
print int('x')
except:
print 'Conversion failed.'
else: # This else means no-except occurred
print 'Conversion successful.'
finally:
print 'Done'
# Run and output
>>>
Converting...
1
Done
Converting...
Conversion failed.
Done
Converting...
Conversion failed.
Done
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