4.7 6 powers of two python

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0 points

about 7 years

my_list = [0,1,2,3,6,5,7]

for i in range[0,len[my_list],2**i]: print my_list[i]

this code gives an error

Answer 55e1c6b5d3292fba3e0000c2

The code is fine apart from the for loop line. Read that line again. for i in range[0, len[my_list], 2**i] means to take the next value from the range and then assign it to i. So first, Python has to generate the range. This means that i can only be assigned a value when the range has been generated. This is how things will go in your case:

1. Python sees the for loop
2. Python tries to generate a range [it doesn’t know what i is yet]
3. It notices that you have passed i to the range[] method, it doesn’t know what i is so it generates a NameError [which basically means that it doesn’t know what i is a name of]

This is how they should have gone:

1. Python sees the for loop
2. It tries to generate a range. Generation is successful.
3. It assigns the first value of the range to i

As you can see, in your case, i has not been created yet and you are already trying to pass it in as an argument to the range[] function. If you tell me what you are trying to do then I could fix your code.

points

about 7 years

Answer 55e28f289113cb1cd400054d

points

about 7 years

Answer 55e3b13b937676a569000576

Try the following:

import math l = list[range[0,100]] for i in range[0, int[math.log[len[l],2]]+1]: print l[2**i - 1]

Note that the last line is indented but does not show in the preview.

points

about 7 years

best way with powers of 2 is using bit-shifting on 1, which is way faster than exponentiation in that case.

That said, I wouldn't recommend a while loop but rather a for loop, or even better: generate your list of values using a list comprehension [which avoids all the variables and undesired side effects, infinite loops because of while, etc...] and one-liner:

print[[1