Python Fibonacci Generator

Question

I need to make a program that asks for the amount of Fibonacci numbers printed and then prints them like 0, 1, 1, 2... but I can't get it to work. My code looks the following:

a = int(raw_input('Give amount: '))

def fib():
    a, b = 0, 1
    while 1:
        yield a
        a, b = b, a + b

a = fib()
a.next()
0
for i in range(a):
    print a.next(),

Solution 1

I would use this method:

Python 2

a = int(raw_input('Give amount: '))

def fib(n):
    a, b = 0, 1
    for _ in xrange(n):
        yield a
        a, b = b, a + b

print list(fib(a))

Python 3

a = int(input('Give amount: '))

def fib(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b

print(list(fib(a)))

Solution 2

You are giving a too many meanings:

a = int(raw_input('Give amount: '))

vs.

a = fib()       

You won't run into the problem (as often) if you give your variables more descriptive names (3 different uses of the name a in 10 lines of code!):

amount = int(raw_input('Give amount: '))

and change range(a) to range(amount).

Solution 3

Since you are writing a generator, why not use two yields, to save doing the extra shuffle?

import itertools as it

num_iterations = int(raw_input('How many? '))
def fib():
    a,b = 0,1
    while True:
        yield a
        b = a+b
        yield b
        a = a+b

for x in it.islice(fib(), num_iterations):
    print x

.....

Solution 4

Really simple with generator:

def fin(n):
    a, b = 0, 1

    for i in range(n):
        yield a
        a, b = b, a + b


ln = int(input('How long? '))
print(list(fin(ln))) # [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...]

Solution 5

Python is a dynamically typed language. the type of a variable is determined at runtime and it can vary as the execution is in progress. Here at first, you have declared a to hold an integer type and later you have assigned a function to it and so its type now became a function.

you are trying to apply 'a' as an argument to range() function which expects an int arg but you have in effect provided a function variable as argument.

the corrected code should be

 a = int(raw_input('Give amount: '))

def fib():
    a, b = 0, 1
    while 1:
        yield a
        a, b = b, a + b

b = fib()
b.next()

for i in range(a):
    print b.next(),

this will work

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Comments

[AgentRev]

fib(0) doesn't yield anything, which can be fixed using range(n+1) instead.

[saeed foroughi]

only code answers are discouraged here. It is encouraged to add some details to how this code will fix the problem.

[Neosapien]

I rewrote this by using a=0, b=1, a=b and b=a+b because I was uncomfortable with that notation but it gave completely different answers. Am I missing something?

[Jyothish Bhaskaran]

I am gettting error on this File "D:\Projects\Python\fibonacci.py", line 18, in <module> b.next() AttributeError: 'generator' object has no attribute 'next'

[Jyothish Bhaskaran]

I found it for Python 3, it is b.__next__(). Sorry :) and Thanks

[Tomerikoo]

Yeah but the question is asking to print the first n numbers, not the nth number...