diff --git a/knowledge base/python.md b/knowledge base/python.md
index 19a326d..45133d0 100644
--- a/knowledge base/python.md	
+++ b/knowledge base/python.md	
@@ -1,13 +1,16 @@
 # Python
 
 1. [TL,DR](#tldr)
-2. [Dictionaries](#dictionaries)
-3. [F-strings](#f-strings)
-4. [Web servers](#web-servers)
+1. [Dictionaries](#dictionaries)
+1. [F-strings](#f-strings)
+1. [Logging](#logging)
+1. [Web servers](#web-servers)
    1. [Flask](#flask)
-   2. [WSGI server](#wsgi-server)
-5. [Further readings](#further-readings)
-6. [Sources](#sources)
+   1. [WSGI server](#wsgi-server)
+1. [Execute commands on the host](#execute-commands-on-the-host)
+1. [Concurrent execution](#concurrent-execution)
+1. [Further readings](#further-readings)
+1. [Sources](#sources)
 
 ## TL,DR
 
@@ -72,6 +75,25 @@ f"Hello, {name}. You are {age}."
 F"{name.lower()} is funny."
 ```
 
+## Logging
+
+Very basic logger:
+
+```py
+import logging
+logging.basicConfig(level=logging.WARNING)
+
+logging.critical("CRITICAL level message")
+logging.exception("ERROR level message")
+logging.error("ERROR level message")
+logging.warning("WARNING level message")
+logging.info("INFO level message")
+logging.debug("DEBUG level message")
+logging.log(level, "{level} level message")
+```
+
+See [logging howto] and [logging library] for more information.
+
 ## Web servers
 
 ### Flask
@@ -128,6 +150,33 @@ pip install flask waitress
 python hello.py
 ```
 
+## Execute commands on the host
+
+Very basic execution:
+
+```py
+import subprocess
+subprocess.call(command)
+```
+
+See [subprocess library] for more information.
+
+## Concurrent execution
+
+Very basic multi-threaded operations:
+
+```py
+from concurrent.futures import ThreadPoolExecutor
+from os import cpu_count
+
+with ThreadPoolExecutor(max_workers=cpu_count()) as executor:
+    for element in elements:
+        logging.debug(f"submitting thread for {element}")
+        executor.submit(function_name, function_arg_1, function_arg_n)
+```
+
+See [concurrent execution] for more information.
+
 ## Further readings
 
 - [Dictionaries]
@@ -137,21 +186,27 @@ python hello.py
 - [Data types]
 - [F-strings]
 - [How to filter list elements in Python]
-- [Logging]
+- [Logging howto]
 - [Flask at first run: do not use the development server in a production environment]
 - [Flask example with POST]
 - [Multi-value query parameters with Flask]
 - [*args and **kwargs in Python]
 - [An intro to threading in Python]
 - [ThreadPoolExecutor in Python: the complete guide]
+- [Concurrent execution]
 
 ## Sources
 
 - [10 python one-liners for dictionaries]
+- [Logging library]
+- [Subprocess library]
 
 <!-- project's references -->
+[concurrent execution]: https://docs.python.org/3/library/concurrency.html
 [dictionaries]: https://docs.python.org/3/tutorial/datastructures.html#dictionaries
-[logging]: https://docs.python.org/3/howto/logging.html
+[logging howto]: https://docs.python.org/3/howto/logging.html
+[logging library]: https://docs.python.org/3/library/logging.html
+[subprocess library]: https://docs.python.org/3/library/subprocess.html
 
 <!-- internal references -->
 [pip]: ./pip.md
diff --git a/scripts/git-all.py b/scripts/git-all.py
index 1196f02..aebb3a6 100755
--- a/scripts/git-all.py
+++ b/scripts/git-all.py
@@ -1,6 +1,10 @@
 #!/usr/bin/env python3
 
-# /usr/bin/env python3 -m pip install --user gitpython
+# Easy, quick & dirty solution to act upon multiple git repositories at once.
+
+# TODO:
+#   - proper commands
+#   - use 'gitpython' instead of calling `git`
 
 import logging
 import subprocess
@@ -10,10 +14,13 @@ from os import cpu_count, getcwd, walk
 from os.path import basename, dirname, isdir
 from sys import argv
 
-log_level = logging.DEBUG
+dry_run = False
+log_level = logging.WARNING
 root_directory = getcwd()
 threads_count = cpu_count()
 
+logging.basicConfig(level=log_level)
+
 def git_command(directory, *args):
     logging.debug(f"thread for {directory}")
     logging.debug(f"using args {args}")
@@ -26,13 +33,20 @@ def git_command(directory, *args):
     command.extend(args)
     logging.debug(command)
 
-    subprocess.call(command)
+    if dry_run is False:
+        subprocess.call(command)
 
 if __name__ == "__main__":
-    if argv[1] == "--debug":
-        logging.basicConfig(level=log_level)
+    if "--debug" in argv:
+        logging.basicConfig(level=logging.DEBUG, force=True)
+        logging.warning("debug mode")
         argv.remove("--debug")
 
+    if "--dry-run" in argv:
+        dry_run = True
+        logging.warning("dry-run mode")
+        argv.remove("--dry-run")
+
     logging.debug(f"using globals {globals()}")
     logging.debug(f"using locals {locals()}")
 
@@ -41,7 +55,9 @@ if __name__ == "__main__":
     if isdir(argv[-1]):
         root_directory = argv[-1]
         git_args = argv[1:-1]
-    else: git_args = argv[1:]
+    else:
+        git_args = argv[1:]
+
     logging.debug(f"starting from {root_directory}")
     logging.debug(f"using git args {git_args}")
 
@@ -51,4 +67,5 @@ if __name__ == "__main__":
     logging.debug(f"creating threads")
     with ThreadPoolExecutor(max_workers=threads_count) as executor:
         for repository in repositories:
+            logging.debug(f"submitting thread for {repository}")
             executor.submit(git_command, repository, *git_args)