Research: Python: Threads and Misc

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@@ -97,6 +97,33 @@ Python encourages polymorphism:
 So remember that when [copying](https://stackoverflow.com/questions/2612802/how-to-clone-or-copy-a-list#2612815)
 or referencing a list.
 
+### Threads
+
+From [GlobalInterpreterLock](https://wiki.python.org/moin/GlobalInterpreterLock):
+
+    In CPython, the global interpreter lock, or GIL, is a mutex that protects
+    access to Python objects, preventing multiple threads from executing Python
+    bytecodes at once. This lock is necessary mainly because CPython's memory
+    management is not thread-safe. (However, since the GIL exists, other features
+    have grown to depend on the guarantees that it enforces.)
+
+    [...]
+
+    The GIL is controversial because it prevents multithreaded CPython programs
+    from taking full advantage of multiprocessor systems in certain situations.
+    Note that potentially blocking or long-running operations, such as I/O, image
+    processing, and NumPy number crunching, happen outside the GIL. Therefore it is
+    only in multithreaded programs that spend a lot of time inside the GIL,
+    interpreting CPython bytecode, that the GIL becomes a bottleneck. 
+
+From: [Thread State and the Global Interpreter Lock](https://docs.python.org/3/c-api/init.html#thread-state-and-the-global-interpreter-lock):
+
+    When threads are created using the dedicated Python APIs (such as the threading
+    module), a thread state is automatically associated to them and the code showed
+    above is therefore correct. However, when threads are created from C (for
+    example by a third-party library with its own thread management), they don’t
+    hold the GIL, nor is there a thread state structure for them.
+
 ### Nice stuff
 
 * [Verbose Regular Expressions](http://www.diveintopython3.net/regular-expressions.html#verbosere).
@@ -120,6 +147,10 @@ or referencing a list.
 
 * [PyCharm](https://www.jetbrains.com/pycharm/).
 
+## Misc
+
+* [Indentation](https://www.python.org/dev/peps/pep-0008/#indentation): Use 4 spaces per indentation level.
+
 ## Test projects
 
 * [Arduino Blog » How close are we to doomsday? A clock is calculating it in real time](https://blog.arduino.cc/2013/03/27/how-close-are-we-to-doomsday-clock/) ([python code](https://github.com/tomschofield/Neurotic-Armageddon-Indicator/blob/master/NAI_SERVER/nai_scraper.py) to parse [Timeline from the Bulletin of the Atomic Scientists](http://thebulletin.org/timeline)).