The document serves as a comprehensive guide on writing functions in Python, covering basics, definitions, and calling functions with positional and keyword arguments. It emphasizes the importance of returning values from functions, providing examples, and encouraging exercises for practice. Advanced topics such as error handling and documentation are also hinted at towards the end.

1. functions!

2. The plan!
Basics: data types (and operations & calculations)
Basics: conditionals & iteration
Basics: lists, tuples, dictionaries
Basics: writing functions
Reading & writing files: opening, parsing & formats
Working with numbers: numpy & scipy
Making plots: matplotlib & pylab
… if you guys want more after all of that …
Writing better code: functions, pep8, classes
Working with numbers: Numpy & Scipy (advanced)
Other modules: Pandas & Scikit-learn
Interactive notebooks: ipython & jupyter
Advanced topics: virtual environments & version control

3. functions
# lets define a function
def print_hello(name):
print "Hello", name, ", it's a nice day for functions!"
# now we can call (or run, or execute) the function
print_hello("Marc")

4. functions
# lets define a function
def print_hello(name):
print "Hello", name, ", it's a nice day for functions!"
# now we can call (or run, or execute) the function
print_hello("Marc") Defining the function:
def function_name(arg1, arg2, ...):
do stuff here
Running the function:
function_name(value1, value2, ...):
indentation!

5. functions
# lets define a function
def print_hello(name):
print "Hello", name, ", it's a nice day for functions!"
# now we can call (or run, or execute) the function
print_hello("Marc")
# let's add some arguments
def print_hello(name, weather):
print "Hello", name, ", it's", weather.
print "Perfect weather for writing functions!"
print_hello("Marc", "Sunny")
print hello("Gengis", "Raining")
# arguments are optional
def print_hello():
print "Hello, this function is a little boring, right?"
# to run a function with 0 arguments, use empty parentheses
print_hello()
Defining the function:
def function_name(arg1, arg2, ...):
do stuff here
Running the function:
function_name(value1, value2, ...):
indentation!

6. functions
# the function definition can be any code!
def print_hello(name, weather, number):
print "Hello", name, ", it's", weather.
if weather == "Sunny":
print "Go outside and play!"
else:
print "Stay inside and program!"
print "Here are some numbers:"
for i in range(number):
print i
print "This is one hell of a long function!"
# nothing happens until the function is run!
print_hello("Marc","Raining", 200)

7. exercise! wohoo!
Write function that takes two arguments: a name and a number. The function then
prints the name "number" time.
---- names.py ----
def name_repeat(????):
????
????
????
name_repeat("Marc", 10)

8. functions: arguments
# positional arguments are defined by their position
def print_hello(name, weather,):
print "Hello", name, ", the weather is", weather.
print_hello("Marc", "Sunny")
print_hello("Stormy", "Thor")

9. functions: arguments
# positional arguments are defined by their position
def print_hello(name, weather,):
print "Hello", name, ", the weather is", weather.
print_hello("Marc", "Sunny")
print_hello("Stormy", "Thor")
# keyword arguments are optional, and have default values.
def print_hello(name, weather, drink= "Tea", snack= "Cookie"):
print "Hello", name, ", the weather is", weather
print "Why don’t you drink a ", drink, "with some", snack
print_hello("Marc", "Sunny", drink="Beer", snack="Tremocos")

10. functions: arguments
# positional arguments are defined by their position
def print_hello(name, weather,):
print "Hello", name, ", the weather is", weather.
print_hello("Marc", "Sunny")
print_hello("Stormy", "Thor")
# keyword arguments are optional, and have default values.
def print_hello(name, weather, drink= "Tea", snack= "Cookie"):
print "Hello", name, ", the weather is", weather.
print "Why don’t you drink a ", drink, "with some", snack
print_hello("Marc", "Sunny", drink="Beer", snack="Tremocos")
Defining arguments:
def function_name(arg1, arg2, … kwarg1=default1, kwarg2=default2, … ):
Code goes here
positional keyword

11. functions: arguments
# positional arguments are defined by their position
def print_hello(name, weather,):
print "Hello", name, ", the weather is", weather.
print_hello("Marc", "Sunny")
print_hello("Stormy", "Thor")
# keyword arguments are optional, and have default values.
def print_hello(name, weather, drink= "Tea", snack= "Cookie"):
print "Hello", name, ", the weather is", weather.
print "Why don’t you drink a ", drink, "with some", snack
print_hello("Marc", "Sunny", drink="Beer", snack="Tremocos")
# keyword arguments are optional, and the order doesn’t matter
print_hello("Bob","Rainy")
print_hello("Bob","Rainy", snack="Cake", drink="Coffee")

12. functions: returning values
# functions are not usually used for printing
# typically they return a value
def times_two_plus_three(x):
return x * 2 + 3
# we can now use this function
n = times_two_plus_three(5)
print n

13. functions: returning values
# functions are not usually used for printing
# typically they return a value
def times_two_plus_three(x):
return x * 2 + 3
# we can now use this function
n = times_two_plus_three(5)
print n
Defining the function:
def function_name(arg1, arg2, ...):
do stuff here
return some_value
Running the function:
answer = function_name(value1, value2, ...):

14. functions: returning values
# functions are not usually used for printing
# typically they return a value
def times_two_plus_three(x):
return x * 2 + 3
# we can now use this function
n = times_two_plus_three(5)
print n
# let's make it a little more complicated.
# and add some documentation as well
def my_complex_calculation(a, b, c):
""" This returns the value of:
a * b + c
"""
result = x * b + c
return result
# we can now use this function
print my_complex_function(8, 1, 12)
Defining the function:
def function_name(arg1, arg2, ...):
""" Documentation (comment)
"""
do stuff here
return some_value
Running the function:
answer = function_name(value1, value2, ...):

15. exercises!
- Write function that takes three inputs (numbers x, y and z), and produces the
result of : a + b - c. Use return to be able to store and use the value later.
---- calc.py ----
def my_calculation(????):
????
????
????
x = my_calculation(12, 13, 14)
print "The complex calculation with 12, 13 and 14 resulted in", x
version 2: as above, but if no numbers for b or c are specified, use 5 and 10 as default
values.