Question about iterating a function in python

Question

I created this function using python

import numpy as np
p1=1/2


def qud(x,p):
    x_sqr = x**2
    x_qud = x**3
    pn=x_sqr*p
    return x_sqr ,x_qud,pn

I need to iterate this function multiple times , by giving the value of pn in the previous iteration.

I tried this without a for loop like this,

First iteration : sqr1, qud1 ,pnew = qud(2,p1)

Second iteration : sqr2, qud2 ,pnew1 = qud(2,pnew)

where i have used the value pnew which obtained from the first iteration.

Third iteration : sqr3, qud3 ,pnew2 = qud(2,pnew1) so on.

Now i wanted to modify my code so that values are going to stored using a for loop , when the number of iterations are given .But my code didnt work.

My code as follows,

i=4
sqr = np.zeros(i)
qud = np.zeros(i)
p1 = np.zeros(i)
sqr[0],qud[0],p1[0] = qud(2,p1)

for j in range (1,3) :
    sqr[j],qud[j],p1[j] = qud(2,p1[j-1])

can any one suggest anything so that this works ?

Thank you

In what way did it not work? Did it throw an exception? Please include the exception here if so. Was it just incorrect? — John
– John, Commented Jul 18, 2019 at 1:08
@Craig That was a typo. When i did using index j too , it didnt work — student_R123
– student_R123, Commented Jul 18, 2019 at 1:14

Mark · Accepted Answer · 2019-07-18 01:09:25Z

3

A pythonic way to do this is to create a generator. The generator will maintain state and you can call next() or use any of the many python itertools, maps, filters, etc. Here's one way to get the first four values:

from itertools import islice

def qud(x,p):
    x_sqr = x**2
    x_qud = x**3
    while True:
        p = x_sqr*p                        # update p
        yield x_sqr ,x_qud,p               # yield instead of return

my_iterator = qud(2,1/2)                   # create an iterator based on itial values

for values in islice(my_iterator, 0, 4):   # loop over an islice 
    print(values)

This will keep making values as long as you keep iterating over it.

answered Jul 18, 2019 at 1:09

Mark

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