Python tutorial: Python3 anonymous functions and lambda Detailed examples of use
Outline
Anonymous function, the name suggests that there is no difference between the maximum function of function, and def defined name that returns the function itself after an anonymous function is created (that is, anonymous functions do not return to the return value), the result is the return value of the expression itself, but after def create is assigned to a variable name, in Python, we create an anonymous function using the keyword lambda, the lambda expression is in the form of an anonymous function:
lambda arg1,arg2,.....argn:expression
The following is a characteristic of some of lambda:
- lambda is an expression, not a statement that we can use in any scene as lambda expressions can be used.
- Lambda is an expression of the body, and that is defined as a function def, lambda also has the function body, but the body is just a lambda expression, so its use functions subject to greater restrictions.
lambda use
No-argument anonymous function
# Lambda can be passed directly to a variable, like the general function call using the same
B = the lambda: True
Print (B ())
# is equivalent to
DEF the BF ():
return True
Print (the BF ())
Sample results:
True
True
There are anonymous function parameters
Support for multiple parameters
No default parameter values
two_sum = lambda x, y: x + y
# 等同于：
def two_sum(x, y): return x + y
print(two_sum(1,2))
Sample results:
3
Parameters with default values
sum_with_100 = lambda x, y=100: x + y
# 等同于：
def sum_with_100(x, y=100): return x + y
print(sum_with_100(200))
Sample results:
300
Parameter passing from behind
The previous example we will assign a variable lambda anonymous function, def embodiment functions similarly defined by transmission parameters, we can pass parameters directly behind lambda:
two_sum = (lambda x, y: x + y)(3, 4)
print(two_sum)
Sample results:
7
Nest
The normal function nested lambda, lambda value of the function itself as the return build a simple closure
sum_with_100 = sum(100)
result = sum_with_100(200)
print(result)
Sample results:
300
Some examples of use
1. The two combined in the minimum valued triplet expression evaluation
lower = lambda x,y: x if x<y else y
print(lower(7,100))
Examples of results:
7
2. The key to a sort of dictionary
= D [{ "order":. 3}, { "order":. 1}, { "order": 2}]
# The order sort key
d.sort (the lambda Key = X: X [ 'order'])
Print (d)
Examples of results
[{'order': 1}, {'order': 2}, {'order': 3}]
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