If a process disappears while iterating the loop in pidstats.reload_threads(), we get a RuntimeError as shown below. This is because we cannot remove an entry from a dictionary while iterating the dictionary. Reproducer: 1. Add the following line to the beginning of pidstats.reload_threads(): import pdb; pdb.set_trace() 2. Start some process 3. Start the python interpreter and proceed as follows: [~/git/python-linux-procfs]$ python3 Python 3.6.8 (default, Jan 3 2019, 16:11:14) [GCC 8.2.1 20181215 (Red Hat 8.2.1-6)] on linux Type "help", "copyright", "credits" or "license" for more information. >>> import procfs >>> ps = procfs.pidstats() >>> ps.reload_threads() > /home/olysonek/git/python-linux-procfs/procfs/procfs.py(462)reload_threads() -> for pid in self.processes.keys(): (Pdb) next > /home/olysonek/git/python-linux-procfs/procfs/procfs.py(463)reload_threads() -> try: At this point, terminate the process started in step 2. Return to the python interpreter: (Pdb) continue Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/olysonek/git/python-linux-procfs/procfs/procfs.py", line 463, in reload_threads try: RuntimeError: dictionary changed size during iteration Signed-off-by: Ondřej Lysoněk <olysonek(a)redhat.com&gt; --- procfs/procfs.py | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/procfs/procfs.py b/procfs/procfs.py index c70fe2a..3423e9e 100755 --- a/procfs/procfs.py +++ b/procfs/procfs.py @@ -458,12 +458,15 @@ class pidstats: self.processes[pid] = process(pid, self.basedir) def reload_threads(self): + to_remove = [] for pid in self.processes.keys(): try: self.processes[pid].load_threads() except OSError: # process vanished, remove it - del self.processes[pid] + to_remove.append(pid) + for pid in to_remove: + del self.processes[pid] def find_by_name(self, name): name = name[:15] --