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Example tutorial on Lambda expressions

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Release： 2017-06-20 15:01:14

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Five exercises for Lambda expressions

Syntax:

Lambda function is an anonymous function, creation syntax:

lambda parameters:express

parameters: Optional, if provided, usually in the form of comma-separated variable expressions, that is, positional parameters.

expression: cannot contain branches or loops (but conditional expressions are allowed), nor can it contain return (or yield) functions. If it is a tuple, it should be enclosed by parentheses .

Call the lambda function, and the result returned is the result of the expression calculation.

1. Question: Use the nesting of conditional operators to complete this question: Students with academic scores >= 90 points are represented by A, between 60-89 points Those with a score of 60 or less are represented by C.

##print( str(score) + ' belongs to ' +

(lambda x:(x>=90 and 'A' or x>= 60 and 'B' or 'C'))(score))

2. Topic: Recursive call of lambda. Split an integer n and print it out. For example, 234 should be printed in three lines: 2, 3, and 4.

n = int(input ())
f=m,f:( (m / 10) !=0 f( int(m/10),f) ( m!=0  print(%(m%10) )))
f(n,f)

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3. Question: Decompose a positive integer into prime factors. For example: input 90, print out 90=2*3*3*5.

Program analysis: To decompose n into prime factors, you should first find a minimum prime number k, and then complete it according to the following steps:

(1) If this prime number is exactly equal to n , it means that the process of decomposing prime factors has ended, just print it out.

(2) If n<>k, but n is divisible by k, the value of k should be printed out, and the quotient of n divided by k should be used as the new positive integer n,

Repeat the first step.

(3) If n is not divisible by k, use k+1 as the value of k and repeat the first step.

import os

import sys
from functools import reduce
from math import sqrt

n = int(input ("Please input a int:\n"))
ans =[]
nn=n
f=lambda m,i,c,f:(m%i ==0 and f(m//i,i,c+1,f) or (m,c))
def func(x,y):
ret,count=f(x,y,0,f )
if count >0:
ans.append(count * [y] )
return ret
reduce(func,[nn]+list(range(2,nn)))
print(ans)

4. Question: Find the value of s=a+aa+aaa+aaaa+aa...a, where a is a number. For example, 2+22+222+2222+22222 (a total of 5 numbers are added at this time), and the addition of several numbers is controlled by the input.

n= int(input("n=:\n"))
aa =a= int(input('a= :\n'))

f=lambda n,a,ans,la,f: n==0 and ans or f(n-1,a,ans+[la* 10+a],la*10+a,f )

print(reduce(lambda x,y:x+y,f(n,aa,[],0,f )))

5. Question: If a number is exactly equal to the sum of its factors, the number is called a "perfect number" ". For example, 6=1+2+3.

Programming: Find all perfect numbers within 1000.

factors = lambda x:filter( lambda i: x%i==0 and i,range(1,x))
f = lambda x: sum(factors(x)) == x
print( [(i,list(factors(i))) for i in list(filter( f, range(2,1001)))])

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