This code below works correct :
JavaScript
x
10
10
1
def file_gen(f_name):2
f = open(f_name)3
for line in f:4
yield line5
6
gen_line = file_gen("foo.html")7
gen_line.next() # '<!DOCTYPE>n'8
gen_line.next() # '<html> n' 9
gen_line.next() # ... next line in file 10
But this function raises StopIteration. I don’t understand why ?
JavaScript
1
9
1
def file_gen(f_name):2
f = open(f_name)3
line = f.readline()4
yield line5
6
gen_line = file_gen('foo.html')7
gen_line.next() # '<!DOCTYPE>n'8
gen_line.next() # StopIteration9
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Answer
You have:
JavaScript
1
5
1
def file_gen(f_name):2
f = open(f_name)3
line = f.readline()4
yield line5
Notice line = f.readline() This only reads 1 line from the file.
Compare:
JavaScript
1
7
1
def g(x):2
li=range(x)3
yield li.pop()4
5
print list(g(10))6
# [9]7
with this:
JavaScript
1
8
1
def g(x):2
li=range(x)3
while li:4
yield li.pop()5
6
print list(g(10))7
# [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]8
yield can only be called once with a particular object or expression. Once it is used by the receiver it must be regenerated. So you need a loop around reading each line of the file.
You can use your second (less readable) form this way:
JavaScript
1
8
1
def file_gen(f_name):2
f = open(f_name)3
while True:4
line = f.readline()5
if not line:6
break7
yield line8
You need a loop to create the the items to yield. In your first case, for line in f: yield line is a loop.
I would rewrite your function this way:
JavaScript
1
5
1
def file_gen(f_name):2
with open(f_name) as f:3
for line in f:4
yield line5