Built-in functions:
Lamba function can be used to sort the dictionary. (No built-in dictionary function, not () Sort by dict.sort)
dic = {'b':5, 'a':3, 'c':4}
# 直接用python函数sorted：
print(sorted(dic))
# output:['a', 'b', 'c']
print(sorted(dic.items())) # 对key排序：
# output:[('a', 3), ('b', 5), ('c', 4)]
print(sorted(dic.items(), key = lambda x:x[1], reverse=True)) # 用lambda函数指定排序元素
# output:[('b', 5), ('c', 4), ('a', 3)]
print(sorted(dic.values())) # 只对值排序
# output:[3, 4, 5]
print(sorted(dic.values(), reverse = True)) # 只对值逆序
# output:[5, 4, 3]List element when the dictionary, you can specify the dictionary elements to sort.
list1 = [
{'name':'joe', 'age':'18'},
{'name':'susan', 'age':'19'},
{'name':'tom', 'age':'17'}
]
print(sorted(list1, key = lambda x:x['name']))
# output:[{'name': 'joe', 'age': '18'}, {'name': 'susan', 'age': '19'}, {'name': 'tom', 'age': '17'}]
print(sorted(list1, key = lambda x:x['age']))
# output:[{'name': 'tom', 'age': '17'}, {'name': 'joe', 'age': '18'}, {'name': 'susan', 'age': '19'}]
Common built-in functions:
| method | description | example |
| abs() | Returns the absolute value function | a = -1 print (abs (num)) # output:1 |
| sorted(list) | Sort, after the return sorted list | print(sorted(['a','b','','d'])) # output:['', 'a', 'b', 'd'] |
| sum(list) | Seeking list of elements and | sum([1,2,3]) # output:6 |
| round(a, b) | Gets the specified number of digits of trees. is a floating-point number, b is the number of bits to be retained | round(3.1415926) # output:3.14 |
| isinstance(a, b) | Type judgment, a is a variable to be determined, b is the type | a = 1 print(isinstance(num,int)) # output:True |
| eval() | Performing an expression, as an arithmetic or string | eval('1+1') # output:2 |
| exec() | Output python statement | exec('print("Python")') # output:Python |
Built-in functions can be queried by dir (__ builtins__).
Higher-order functions:
| method | description |
| map(func, seq[,seq[,seq...]]) - > list |
Receiving a set of functions and a plurality of sequences, it will be provided as a function of mapping the specified sequence, and then returns a new map object. |
| filter(func, seq) - > list or tuple or string |
Sequences for filtering, the filter element does not conform to the conditions, the object returned by the qualified filter elements. |
| reduce(func, seq[, initvalue]) | For all elements of a sequence of data calls func merge operation may be given an initial value. |
map：
Example 1:
list1 = [1,2,3,4,5]
# map
new_list = map(lambda x:x*2, list1)
print(new_list)
# output:<map object at 0x0000013AB0630128>
print(list(new_list)) # 将map对象转换为list
# output:[2, 4, 6, 8, 10]
# 或者
print([x*2 for x in list1])
# output:[2, 4, 6, 8, 10]Example 2:
list1 = [1,3,5,7,9]
list2 = [2,4,6,8,10]
# map
new_list = map(lambda x, y : x*y, list1, list2)
print(new_list)
# output:<map object at 0x0000013AB0630128>
print(list(new_list)) # 将map对象转换为list
# output:[2, 12, 30, 56, 90]
# 即对应元素相乘
# 或者
print([x*y for x,y in zip(list1, list2)])
# output:[2, 12, 30, 56, 90]filter:
Example 1:
list1 = [1,3,5,7,9]
# filter
new_list = filter(lambda x : x>4, list1)
print(new_list)
# output:<filter object at 0x0000013AB0692470>
print(list(new_list)) # 将map对象转换为list
# output:[5, 7, 9]
# 或者
print([x for x in list1 if x > 4])
# output:[5, 7, 9]The above filter into a map:
new_list = map(lambda x : x>4, list1)
print(list(new_list)) # 将map对象转换为list
# output:[False, False, True, True, True]All, map indicate map, filter represents the screening, the two are not interchangeable.
reduce：
Example:
from functools import reduce
list2 = [2,4,6,8,10]
reduce(lambda x,y:x+y, list2)
# output:30
# x+y: 2+4, 返回6
# x+y: 6+6, 返回12
# x+y: 12+8,返回20
# x+y: 20+20,返回30
reduce(lambda x,y:x+y, list2, 5)
# output:35
# x+y: 5+2, 返回7
# x+y: 7+4, 返回11
# ……