@@ -0,0 +1,127 @@
+# Handy classes in the standard library
+
+So far we have learned to use lists, tuples and dictionaries. They are 
+commonly used data types in Python. The standard library contains more 
+handy types that behave a lot like the datatypes that we know already. 
+You can always use the built-in types instead of the collections module, 
+but sometimes the collections module makes everything a lot easier.
+
+## Sets
+
+Let's say we have two lists of strings
+
+```python
+
+```
+
+## Named tuples
+
+It can be tempting to make a class that just contains a bunch of data 
+and that's it.
+
+```python
+class Website:
+
+    def __init__(self, url, founding_year, free_to_use):
+        self.url = url
+        self.founding_year = founding_year
+        self.free_to_use = free_to_use
+
+
+github = Website('https://github.com/', 2008, True)
+```
+
+You should avoid making classes like this. This class has only one 
+method, so it doesn't really need to be a class. We could just use a 
+tuple instead:
+
+```python
+github = ('https://github.com/', 2008, True)
+```
+
+The problem with this is that if someone reading our code sees something 
+like `website[1] > 2010` it's not going to make much sense, like 
+`website.founding_year > 2010` would.
+
+In cases like this, `collections.namedtuple` is handy:
+
+```python
+>>> Website = collections.namedtuple('Website', 'url founding_year free_to_use')
+>>> github = Website('https://github.com/', 2008, True)
+>>> github[1]
+2008
+>>> for thing in github:
+...     print(thing)
+... 
+https://github.com/
+2008
+True
+>>> github.founding_year
+2008
+>>> github
+Website(url='https://github.com/', founding_year=2008, free_to_use=True)
+>>> print(github)
+Website(url='https://github.com/', founding_year=2008, free_to_use=True)
+>>>
+```
+
+As you can see, our `github` behaves like a tuple, but 
+`github.founding_year` also works and `github` looks nice when we have a 
+look at it on the `>>>` prompt or we print it.
+
+## Deques
+
+To understand deques, we need to first learn about a list method I 
+haven't talked about earlier. It's called `pop` and it works like this:
+
+```python
+>>> names = ['wub_wub', 'theelous3', 'Nitori', 'RubyPinch', 'go|dfish']
+>>> names.pop()
+'go|dfish'
+>>> names
+['wub_wub', 'theelous3', 'Nitori', 'RubyPinch']
+>>> names.pop()
+'RubyPinch'
+>>> names
+['wub_wub', 'theelous3', 'Nitori']
+>>> names.pop()
+'Nitori'
+>>> names
+['wub_wub', 'theelous3']
+```
+
+As you can see, the list shortens by one from the end when we pop from 
+it, and we also get the removed value back. So now we know that we can 
+add an item to the end of a list using `append`, and we can remove an 
+item from the end using `pop`.
+
+It's also possible to do this in the beginning of a list, but lists were 
+not designed to be used that way and it would be slow if our list would 
+be big.
+
+The `collections.deque` class makes appending and popping from both ends 
+easy and fast. It works just like lists, but it also has `appendleft` 
+and `popleft` methods.
+
+```python
+>>> names = collections.deque(['theelous3', 'Nitori', 'RubyPinch'])
+>>> names
+deque(['theelous3', 'Nitori', 'RubyPinch'])
+>>> names.appendleft('wub_wub')
+>>> names.append('go|dfish')
+>>> names
+deque(['wub_wub', 'theelous3', 'Nitori', 'RubyPinch', 'go|dfish'])
+>>> names.popleft()
+'wub_wub'
+>>> names.pop()
+'go|dfish'
+>>> names
+deque(['theelous3', 'Nitori', 'RubyPinch'])
+>>> 
+```
+
+Deques are often used as queues. It means that items are always added to 
+one end and popped from the other end.
+
+
+**TODO:** add some of ChainMap, Counter, OrderedDict, defaultdict, deque, sets
@@ -16,11 +16,11 @@ the instructions using a **programming language**. Most programming
 languages consist of English words, digits and some characters that have
 special meanings.
 
-Unlike people often think, **programming is not complicated**. Large
-programs are always made of small, simple pieces, and those pieces are
-written one by one. Programming languages are made to be used by humans,
-so if there's an easy way to do something and a difficult way to do
-something, you should use the easier way.
+Unlike people often think, programming is usually not complicated. Large
+programs are always made of **small, simple pieces**, and those pieces
+are written one by one. Programming languages are made to be used by
+humans, so if there's an easy way to do something and a difficult way to
+do something, you should use the easier way.
 
 ## What do I need?
 
@@ -33,10 +33,10 @@ You also don't need a powerful computer. I could do almost all of my
 programming on a 12-year-old computer if I needed to. Fast computers are
 nice to work with, but you don't need them.
 
-Programming takes time like all hobbies do. Some people learn it
-quickly, and some people don't. I don't expect you to read this tutorial
-in a couple hours and then master everything it's talking about. Take
-your time with things, and remember that I learned to program slowly.
+Programming takes time like all hobbies do. Some people learn it 
+quickly, and some people don't. I don't expect you to read this tutorial 
+in a couple hours and then master everything it's talking about. Take 
+your time with things, and remember that I learned to program slowly. 
 
 ## Getting started
 
@@ -105,10 +105,10 @@ should you do if you have a problem with the tutorial?
 2. Read the code and the explanation for it again.
 3. If there's something you haven't seen before in the tutorial and it's
     not explained, try to find it from the previous chapters.
-4. If you still have trouble understanding the tutorial or any other problems
-    with the tutorial, please [tell me about it](../contact-me.md). I want to
-    improve this tutorial so other readers won't have the same problem as you
-    have.
+4. If you can't find what you're looking for or you still have trouble 
+   understanding the tutorial or any other problems with the tutorial, 
+   please [tell me about it](../contact-me.md). I want to improve this 
+   tutorial so other readers won't have the same problem as you have.
 5. See [Getting help](../getting-help.md) if you can't contact me for some
     reason.