Adds talk from Jack Diederich

Author: kushaldas

docs/functions.rst

@@ -3,7 +3,10 @@
 Functions
 =========
 
-Reusing the same code is required many times within a same program. Functions help us to do so. We write the things we have to do repeatedly in a function then call it where ever required. We already saw build in functions like *len()*, *divmod()*.
+Reusing the same code is required many times within a same program. Functions
+help us to do so. We write the things we have to do repeatedly in a function
+then call it where ever required. We already saw build in functions like
+*len()*, *divmod()*.
 
 Defining a function
 ===================
@@ -16,22 +19,26 @@ We use *def* keyword to define a function. General syntax is like
         statement1
         statement2
 
-Let us write a function which will take two integers as input and then return the sum.
+Let us write a function which will take two integers as input and then return
+the sum.
 
 ::
 
     >>> def sum(a, b):
     ...     return a + b
 
-In the second line with the *return* keyword, we are sending back the value of *a + b* to the caller. You must call it like
+In the second line with the *return* keyword, we are sending back the value of
+*a + b* to the caller. You must call it like
 
 ::
 
     >>> res = sum(234234, 34453546464)
     >>> res
     34453780698L
 
-Remember the palindrome program we wrote in the last chapter. Let us write a function which will check if a given string is palindrome or not, then return *True* or *False*.
+Remember the palindrome program we wrote in the last chapter. Let us write a
+function which will check if a given string is palindrome or not, then return
+*True* or *False*.
 
 ::
 
@@ -72,7 +79,13 @@ The output
     inside change function 90
     After the function call  9
 
-First we are assigning *9* to *a*, then calling change function, inside of that we are assigning *90* to *a* and printing *a*. After the function call we are again printing the value of *a*. When we are writing *a = 90* inside the function, it is actually creating a new variable called *a*, which is only available inside the function and will be destroyed after the function finished. So though the name is same for the variable *a* but they are different in and out side of the function.
+First we are assigning *9* to *a*, then calling change function, inside of that
+we are assigning *90* to *a* and printing *a*. After the function call we are
+again printing the value of *a*. When we are writing *a = 90* inside the
+function, it is actually creating a new variable called *a*, which is only
+available inside the function and will be destroyed after the function finished.
+So though the name is same for the variable *a* but they are different in and
+out side of the function.
 
 ::
 
@@ -87,7 +100,9 @@ First we are assigning *9* to *a*, then calling change function, inside of that
     change(a)
     print("After the function call ", a)
 
-Here by using global keyword we are telling that *a* is globally defined, so when we are changing a's value inside the function it is actually changing for the *a* outside of the function also.
+Here by using global keyword we are telling that *a* is globally defined, so
+when we are changing a's value inside the function it is actually changing for
+the *a* outside of the function also.
 
 The output
 ::
@@ -100,7 +115,8 @@ The output
 Default argument value
 ======================
 
-In a function variables may have default argument values, that means if we don't give any value for that particular variable it will be assigned automatically.
+In a function variables may have default argument values, that means if we don't
+give any value for that particular variable it will be assigned automatically.
 
 ::
 
@@ -110,7 +126,9 @@ In a function variables may have default argument values, that means if we don't
     ...     else:
     ...         return False
 
-In the above example we have written *b = -99* in the function parameter list. That means if no value for *b* is given then b's value is *-99*. This is a very simple example of default arguments. You can test the code by
+In the above example we have written *b = -99* in the function parameter list.
+That means if no value for *b* is given then b's value is *-99*. This is a very
+simple example of default arguments. You can test the code by
 
 ::
 
@@ -123,7 +141,8 @@ In the above example we have written *b = -99* in the function parameter list. T
 
    Remember that you can not have an argument without default argument if you already have one argument with default values before it. Like *f(a, b=90, c)* is illegal as *b* is having a default value but after that *c* is not having any default value.
 
-Also remember that default value is evaluated only once, so if you have any mutable object like list it will make a difference. See the next example
+Also remember that default value is evaluated only once, so if you have any
+mutable object like list it will make a difference. See the next example
 
 ::
 
@@ -153,7 +172,7 @@ To avoid this you can write more idiomatic Python, like the following
     >>> print(f(2))
     [2]
 
-.. note:: To understand more read `this link <http://docs.python.org/2/tutorial/controlflow.html#default-argument-values>`_.
+.. note:: To understand more read `this url <https://docs.python.org/3/tutorial/controlflow.html#default-argument-values>`_.
 
 Keyword arguments
 =================
@@ -169,7 +188,10 @@ Keyword arguments
     >>> func(b=12, c = 24, a = -1)
     a is -1 and b is 12 and c is 24
 
-In the above example you can see we are calling the function with variable names, like *func(12, c = 24)*, by that we are assigning *24* to *c* and *b* is getting its default value. Also remember that you can not have without keyword based argument after a keyword based argument. like
+In the above example you can see we are calling the function with variable
+names, like *func(12, c = 24)*, by that we are assigning *24* to *c* and *b* is
+getting its default value. Also remember that you can not have without keyword
+based argument after a keyword based argument. like
 
 ::
 
@@ -182,8 +204,9 @@ In the above example you can see we are calling the function with variable names
 Keyword only argument
 =====================
 
-We can also mark the arguments of function as keyword only. That way while calling the function, the user will be forced to use
-correct keyword for each parameter.
+We can also mark the arguments of function as keyword only. That way while
+calling the function, the user will be forced to use correct keyword for each
+parameter.
 
 ::
 
@@ -204,7 +227,9 @@ correct keyword for each parameter.
 Docstrings
 ==========
 
-In Python we use docstrings to explain how to use the code, it will be useful in interactive mode and to create auto-documentation. Below we see an example of the docstring for a function called *longest_side*.
+In Python we use docstrings to explain how to use the code, it will be useful in
+interactive mode and to create auto-documentation. Below we see an example of
+the docstring for a function called *longest_side*.
 
 
 ::
@@ -254,8 +279,9 @@ In Python any function can act as higher order function.
 map function
 =============
 
-`map` is a very useful higher order function in Python. It takes one function and an iterator
-as input and then applies the function on each value of the iterator and returns a list of results.
+`map` is a very useful higher order function in Python. It takes one function
+and an iterator as input and then applies the function on each value of the
+iterator and returns a list of results.
 
 Example::
 
@@ -267,3 +293,10 @@ Example::
     >>> print(list(map(square, lst)))
     [1, 4, 9, 16, 25]
 
+
+HOWTO Write a function
+========================
+
+Watch `this talk <https://www.youtube.com/watch?v=rrBJVMyD-Gs>`_ by Jack
+Diederich at PyCon US 2018 to learn more about how to write clean Python
+functions and many other tips.