How to convert generator object into list?

Question

My code

def yieldlines(thefile, whatlines):
  return (x for i, x in enumerate(thefile) if i in whatlines)

file1=open('/home/milenko/EDIs/site1/newst2.txt','r')
whatlines1 = [line.strip() for line in open('m1.dat', 'r')]

x1=yieldlines(file1, whatlines1)

print x1

I got

<generator object <genexpr> at 0x7fa3cd3d59b0>

Where should I put the list,or I need to rewrite the code?

I want my program to pen the file and read the content so for specific lines that are written in m1.dat.I have found that solution Reading specific lines only (Python)

Please explain exactly what you are trying to do. Because what you just got is a [generator](https://www.python.org/dev/peps/pep-0289/) and there is nothing *really* wrong. If you iterate over it you will get your output. But there are differences you need to be aware of. Make sure you read the link I provided. — idjaw, Mar 14 '16 at 19:24

score 42 · Accepted Answer · answered Mar 14 '16 at 19:27

42

If you actually need a list, you can just do:

lst = list(generator_object)

However, if all you want is to iterate through the object, you do not need a list:

for item in generator_object:
    # do something with item

For example,

sqr = (i**2 for i in xrange(10)) # <generator object <genexpr> at 0x1196acfa0>
list(sqr) # [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

sqr = (i**2 for i in xrange(10))
for x in sqr:
    print x,
# 0 1 4 9 16 25 36 49 64 81

answered Mar 14 '16 at 19:27

Julien Spronck

15,069
4
47
55

No.with print list(x1),I got only [].Why? – Richard Rublev Mar 14 '16 at 19:35
Your generator must be empty. either `thefile` is empty or no line satisfied the condition. – Julien Spronck Mar 14 '16 at 19:37

score 4 · Answer 2 · answered Mar 14 '16 at 19:28

4

To convert a generator expression into a list it is sufficient to do:

list(<generator expression>)

Beware though if the generator expression can generate an infinite list, you will not get what you expect.

answered Mar 14 '16 at 19:28

Mats Kindahl

1,863
14
25

How to convert generator object into list?

2 Answers2