What is the current value of a Python itertools counter

Question

The itertools.count counter in Python (2.7.9) is very handy for thread-safe counting. How can I get the current value of the counter though?

The counter increments and returns the last value every time you call next():

import itertools
x = itertools.count()
print x.next()  # 0
print x.next()  # 1
print x.next()  # 2

So far, so good.

I can't find a way to get the current value of the counter without calling next(), which would have the undesirable side-effect of increasing the counter, or using the repr() function.

Following on from the above:

print repr(x)  # "count(3)"

So you could parse the output of repr(). Something like

current_value = int(repr(x)[6:-1])

would do the trick, but is really ugly.

Is there a way to get the current value of the counter more directly?

Answer 1

Another hack to get next value without advancing iterator is to abuse copy protocol:

>>> c = itertools.count()
>>> c.__reduce__()[1][0]
0
>>> next(c)
0
>>> c.__reduce__()[1][0]
1

Or just take it from object copy:

>>> from copy import copy
>>> next(copy(c))
1

Answer 2

Use the source, Luke!

According to module implementation, it's not possible.

typedef struct {
    PyObject_HEAD
    Py_ssize_t cnt;
    PyObject *long_cnt;
    PyObject *long_step;
} countobject;

Current state is stored in cnt and long_cnt members, and neither of them is exposed in object API. Only place where it may be retrieved is object __repr__, as you suggested.

Note that while parsing string you have to consider a non-singular increment case. repr(itertools.count(123, 4)) is equal to 'count(123, 4)' - logic suggested by you in question would fail in that case.

Answer 3

According to the documentation there is no way to access the current value of the function. itertools.count() is a generator method from the itertools module. As such, it is common practice to just simply assign the value of a generator's current value to a variable.

Simply store the the result of the next call:

current_value = x.next()

or ( Built-in python method for Python version ≥ 2.6 )

current_value = next(x)

You could make a wrapper function, or a utility decorator class if you would like some added syntactic sugar, but assignment is standard.