python tricks

1.

cities = ['Marseille', 'Amsterdam', 'New York', 'Londom']

# the good way
for i, city in enumerate(cities):
    print(i, city)

2.

x_list = [1, 2, 3]
y_list = [2, 4, 6]

# the good way
for x, y in zip(x_list, y_list):
    print (x, y)

3.

x = 10
y = -10

# the good way
x, y = y, x
print ('After: x = %d, y = %d' % (x, y))

4.

ages = {
    'Mary'      : 31,
    'Honathan' : 28
}

# the good way
age = ages.get('Dick', 'Unknow')
print ('Dick is %s years old' % age)

5.

needle = 'd'
haystack = ['a', 'b', 'c', 'd']
# the good way
for letter in haystack:
    if needle == letter:
        print ('Found!')
        break
else:
    print ('Not found!')

6.

# the good way
with open('pimpin-aint-easy.txt') as f:
    for line in f:
        print (line)

7.

print ('Converting!')
try:
    print (int('1'))
except:
    print ('Conversion failed!')
else:
    print ('Conversion uccessful!')
finally:
    print ('Done!')

 8.

普通的方法，第一个参数需要是self，它表示一个具体的实例本身。
如果用了staticmethod，那么就可以无视这个self，而将这个方法当成一个普通的函数使用。
而对于classmethod，它的第一个参数不是self，是cls，它表示这个类本身。
>>> class A(object):
    def foo1(self):
        print "Hello",self
    @staticmethod
    def foo2():
        print "hello"
    @classmethod
    def foo3(cls):
        print "hello",cls

9.  Goal: Check if my version is the latest

lastest_python = 3
my_python = 2
msg = 'Update available' if lastest_python > my_python else 'Up to daye'
print('Update check: {}'.format(msg))

latest_python = [3, 5, 2]
my_python = [3, 5, 1]
msg = 'Update available' if latest_python > my_python else 'Up to date'
print('Update check: {}'.format(msg)

10. python之字符串格式化(format)

用法：

　　它通过{}和:来代替传统%方式

1、使用位置参数

要点：从以下例子可以看出位置参数不受顺序约束，且可以为{},只要format里有相对应的参数值即可,参数索引从0开，传入位置参数列表可用*列表

>>> li = ['hoho',18]
>>> 'my name is {} ,age {}'.format('hoho',18)
'my name is hoho ,age 18'
>>> 'my name is {1} ,age {0}'.format(10,'hoho')
'my name is hoho ,age 10'
>>> 'my name is {1} ,age {0} {1}'.format(10,'hoho')
'my name is hoho ,age 10 hoho'
>>> 'my name is {} ,age {}'.format(*li)
'my name is hoho ,age 18'

2、使用关键字参数

要点：关键字参数值要对得上，可用字典当关键字参数传入值，字典前加**即可

>>> hash = {'name':'hoho','age':18}
>>> 'my name is {name},age is {age}'.format(name='hoho',age=19)
'my name is hoho,age is 19'
>>> 'my name is {name},age is {age}'.format(**hash)
'my name is hoho,age is 18'

3、填充与格式化

:[填充字符][对齐方式 <^>][宽度]

>>> '{0:*>10}'.format(10)  ##右对齐
'********10'
>>> '{0:*<10}'.format(10)  ##左对齐
'10********'
>>> '{0:*^10}'.format(10)  ##居中对齐
'****10****'

4、精度与进制

>>> '{0:.2f}'.format(1/3)
'0.33'
>>> '{0:b}'.format(10)    #二进制
'1010'
>>> '{0:o}'.format(10)     #八进制
'12'
>>> '{0:x}'.format(10)     #16进制
'a'
>>> '{:,}'.format(12369132698)  #千分位格式化
'12,369,132,698'

5、使用索引

>>> li
['hoho', 18]
>>> 'name is {0[0]} age is {0[1]}'.format(li)
'name is hoho age is 18

11.  Goal: Check if my version is the latest

# Ordered by population
cities = ['Groningen', 'Marseille', 'Paries', 'Buenos Aires', 'Mumbai']

smallest, *rest, largest = cities

print('smallest: {}'.format(smallest))
print('largest: {}'.format(largest))

12.  未知数量参数

def draw_curve(*curves):
    fig, axes = plt.subplots(nrows=1, figsize=(10, 8))
    for curve_i, curve_name in enumerate(curves):
    。。。