#                                                     lists.py

# Remember that a string is an ordered set of characters?  Well, a list is
# an ordered set of values of any type.  Both strings and lists and other
# things that behave like ordered sets are called sequences.

# Since a list is a data structure, think about four things that I talked
# about when I introduced strings to you:
#   (1) How do you create one?
#   (2) How do you access an element in it?
#   (3) How do you modify an element in it in place?
#   (4) How do you destroy it when we don't need it any more? (don't worry
#       about it)


# Let's see some lists and related functions that we can use to manipulate
# lists.  Also think about where lists would be useful as you write your
# programs.


# Create a list on the fly and print it to the standard output device
#
print [10, 20, 30, 40, 50]

# Once more with different type of elements
#
print ["Let", "us", "stop", "spams"]

# Once more with an element itself as a list
#
print ["hello", 2.0, 5, ["nested", 2, 5]]


# Here is another way of creating a list, 1 inclusive, 7 exclusive
#
print range(1, 7)


# From 0 to 9 inclusive
#
print range(10)

# 1 to 10 in 2 or 3 increments
#
print range(1, 10, 2)

print range(1, 10, 3)


# Let's see how we access elements in a list

# First create a list
#
numbers = [10, 20, 30, 40, 50]

# Make sure it is created as expected
#
print numbers

# Remember that strings are immutable?
# Well, lists are mutable, which means that we can modify an element in
# a list in place.  This is the syntax that you use to do it.
# 
numbers[2] = 3

# Let's see if indeed the modification is done in place.
#
print numbers

# Use a for loop as we did with a string
#
for n in numbers:
    print n


# Concatenating two lists together

a = [1, 2, 3]
b = [3, 4, 5]

print a + b


# What would you expect this to do?  Well, verify your answer by running it
#
print [0] * 4

# How about this one?  Again run it to see what it does
#
print [1, 2, 3] * 3


# Slicing lists, much like we did with strings
#

a_list = ['a', 'b', 'c', 'd', 'e', 'f']

# 1 inclusive, 3 exclusive
#
print a_list[1:3]

print a_list[:4]

print a_list[3:]

print a_list[:]


# deleting elements of a list
#

del a_list[2]
print a_list


del a_list[2:4]
print a_list


# Inserting elements into a list - this would be useful enough to create a
# function for it.
#
def insert(u, v, i):
    u[i:i] = v

print numbers

insert(numbers, [111], 1)
print numbers

insert(numbers, [22, 33, 44], 2)
print numbers


# Converting strings to lists - sometimes it is useful to convert a string
# into a list and manipulate it as a list.
#

print list("Stop that!")


# Some basic functions dealing with lists
#
def del_head(u):
    del u[0]

aa = [1, 2, 3, 4, 5]

del_head(aa)

print aa



def tail(u):
    return u[1:]

print tail(aa)

print aa


x = range(1, 11)

print x

# What does this do? For each element in x double it and include them all in
# a list - neat, huh?
#
y = [j * 2 for j in x]

print y



# Matrix

# | 1 2 3 |
# | 4 5 6 |
# | 7 8 9 |

m = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

print "m[1] = ", m[1]

m[1] = [10, 20, 30]

print "m[1] = ", m[1]


print "m[1][2] = ", m[1][2]


m[1][2] = 300

print "m[1][2] = ", m[1][2]

print


# We can print the 3 rows in order like this:
#
for r in m:
    print r

print

# We can print the 9 elements in order like this:
#
for r in m:
    for e in r:
        print e


# This is a rather inefficient way to deal with matrices in Python.  Later,
# toward the end of this tutorial we will learn a more efficient way using
# Scipy and Numpy.



# Exercise 1:
#
# See Section 9.22 of [DEM] if you want to see some exercise problems.