Methods in a generator expression: gi_running, gi_yieldfrom, etc

David542 :

I have created the following generator function:

>>> def file_readlines(filepath):
...     f = open(filepath, 'r')
...     for line in f:
...         yield line
... 
>>> gen=file_readlines(filepath)
>>> next(gen)

When I examine the methods of the generator it shows the following:

...'close', 'gi_code', 'gi_frame', 'gi_running', 'gi_yieldfrom', 'send', 'throw'`

throw, send, and close are documented in Python Expressions, and I imagine code and frame are similar to a stacktrace object, but what are gi_running and gi_yieldfrom? How are those used?

Patrick Haugh :

gi_running tells you whether or not the interpreter is currently executing instructions from the frame of the generator (gi_frame)

gi_yieldfrom is the iterator that the generator is yielding from. It was introduced in 3.5, and you can read the enhancement ticket here: https://bugs.python.org/issue24450

def yielder(gen):
    yield from gen

x = range(5)  
g = yielder(x)

print(g.gi_yieldfrom) # None
next(g) # delegate to the other iterator
print(g.gi_yieldfrom) # <range_iterator object at 0x0000026A0D72C830>
list(g) # exhaust iterator
print(g.gi_yieldfrom) # None