On 14/03/13 08:12, Abhishek Pratap wrote:
import numpy as np
count = 0
[ count += 1 for num in np.random.random_integers(1,100,20) if num > 20]
File "<ipython-input-45-0ba0e51b7644>", line 2
[ count += 1 for num in np.random.random_integers(1,100,20) if num > 20]
^
SyntaxError: invalid syntax
[...]
I just used a very contrived example to ask if we can increment a
counter inside a generator. The real case is more specific and
dependent on other code and not necessarily useful for the question.
Not everything can happen inside a list comprehension or generator
comprehension.
They are both deliberately kept simple, and can only include an expression.
Since count += 1 is not an expression, you cannot use it directly inside a list
comp. Some possible solutions:
1) wrap it in a helper function:
count = 0
def incr():
global count
count += 1
values = [incr() or expr for num in np.random.random_integers(1, 100, 20) if num
> 20]
2) Use a for loop:
count = 0
for num in np.random.random_integers(1, 100, 20):
if num > 20:
count += 1
3) Use len:
values = [num for num in np.random.random_integers(1, 100, 20) if num > 20]
# or if you prefer:
# values = filter(lambda x: x > 20, np.random.random_integers(1, 100, 20))
count = len(values)
4) Use sum:
count = sum(1 for num in np.random.random_integers(1, 100, 20) if num > 20)
--
Steven
_______________________________________________
Tutor maillist - [email protected]
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
