Add notes on pdb and local and remote debugging with vscode

session_10_debugging/debugging.md

+# Debugging in Python
+
+## Some concepts
+
+* *Breakpoint* - location in a file where the debugger should pause
+* *Continue* - resume execution until next breakpoint or unexpected condition
+* *Step over* - execute the current line and pause at the beginning of the next
+* *Step into* - if the current line is a function call, enter the function and execute from the first line of the function
+* *Step out* - execute the current function till the end and pause as soon as the function returns
+* *Backtrace* - the execution path up to the location where the debugger is paused
+
+## `pdb` cheat sheet
+
+* `args` - show arguments from surrounding function
+* `b` & `break` - set or list breakpoints
+* `display` - show tracked variables
+* `n` & `next` - execute instruction in next line (step over)
+* `s` & `step` - execute next possible instruction (step into)
+* `r` & `return` - execute until end of current function (step out)
+* `p` & `pp` - print result of expression
+* `ll` & `longlist` - show the source code/context of current paused state
+* `bt` & `w` & `where` - show the execution path up to the current location
+
+## launching pdb
+
+Add `import pdb ; pdb.set_trace()` to your code and you will get access to `pdb` on the spot.
+
+Alternatively run `python -mpdb script.py` from the command-line.
+
+## VSCode / VSCodium
+
+Install [Python extension](https://marketplace.visualstudio.com/items?itemName=ms-python.python) by Microsoft to have Python goodies and debugging powers.
+
+## Remote debugging & development
+
+The [remote development pack](https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.vscode-remote-extensionpack) is pretty awesome. You might find the [Remote - SSH](https://aka.ms/vscode-remote/download/ssh) option very useful, together with the [Remote - Containers](https://aka.ms/vscode-remote/download/containers) if you work with a lot with docker and similar solutions.
+
+### Reaching the location where the code is running
+
+This requires some familiarity with network concepts and `SSH`.
+
+You will need to setup port-forwarding (aka tunneling) using `SSH`.  
+You might also need to `ProxyJump` a few computers to get to the location where the code is running.
+
+A simple, "one hop" `SSH` tunnel can be achieved with `ssh -L localhost:5678:localhost:5678 login.cluster.embl.de`.
+
+For more about SSH tunnels try [these docs](https://www.ssh.com/ssh/tunneling/example) and [how to use `ProxyJump`](https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Proxies_and_Jump_Hosts#Passing_Through_One_or_More_Gateways_Using_ProxyJump).
+
+### debugpy
+
+`debugpy` is [pretty awesome](https://github.com/microsoft/debugpy) but needs to connect via the network. You'll need to use the `SSH` tunnel setup above.
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session_10_debugging/debugging.py

+import os
+import glob
+
+
+def split(path):
+    return path.rsplit("/", 1)
+
+
+def get_path(filename):
+    head, tail = split(filename)
+    return os.path.abspath(head)
+
+
+def main(hostname):
+    extension = "one/**/*.py"
+    files = glob.glob(extension, recursive=True)
+    path = get_path(files[0])
+    print(">>>>", path, "<<<< on", hostname)
+
+
+if __name__ == "__main__":
+    hostname = os.uname().nodename
+    if hostname == "login.cluster.embl.de":
+        import debugpy
+        print("debugpy loaded and waiting for connection")
+        debugpy.listen(12125)
+        debugpy.wait_for_client()
+        print("debugpy session active")
+
+    main(hostname)
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session_10_debugging/one/test/file/too/many/debugging.py

+../../../../../debugging.py
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