#!/usr/bin/env python
# coding: utf-8

# # Python Clase 3: Strings and Lists

# # Strings
# 
# A sequence of characters

# In[6]:


s = 'hellou, how are you?'


# In[7]:


type(s)


# ### string - immutable object
# cannot modify it

# In[42]:


s[1] = 'a'


# Everything in python is Oriented Object (oo)
# 
# s is an object and one can apply a method

# In[8]:


s.capitalize(), s.upper()                  #OO - s.method()


# In[9]:


s.count('o'), s.count('ou')               #we'll see later more aboyt regular expressions


# In[19]:


s.replace('o','i')                        #**  see murcielago's homework


# In[43]:


s.replace('e', 'a', 1)                 #solamente una vez


# In[13]:


s.split(' ')                             #what happen with helliu? immutable object, strings dont change


# In[17]:


b = 'hello \t' + "how \n " + 'are' + 'you'*2   # they can 'sum' and 'multiply'


# In[18]:


print b


# In[20]:


c = 'roma'                               #** See anagramas' work
d ='amor'


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sorted(c) == sorted(d)


# ## Cadenas con eslavones

# In[23]:


s                                       


# In[26]:


len(s)


# ### indexing

# In[27]:


s[0], s[1]


# In[29]:


s[0:6], s[:6]                             #print only hellou


# In[30]:


s[16:20]                                #only imprimir you?


# In[32]:


s[-1]                                    #indices can start counting from the end


# In[33]:


s[-4:]


# In[34]:


s.split(' ')[-1]                         #we'll see more on 'lists' section


# In[35]:


j =0
for i in s:                              #usual ex. is to print by pairs
    if j%2 ==0: print i
    j+=1


# ### Slicing

# In[36]:


s[::2]                      #in python, that's easy. Example: print every 3 from 9 to 16


# In[37]:


s[::-1]                    #ex. print upside-down --- Exercise: do it by hand


# #### Palindromo ?

# In[38]:


pal = 'anita lava la tina'          #why  pal != pal[::-1]?


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pal2 = pal.replace(' ', '') 


# In[40]:


pal2 == pal2[::-1]          

#Examples:
# Some men interpret nine memos 
# Was it a cat I saw?
# O, a kak Uwakov lil vo kawu kakao!


# ## Format string syntax
# 
# printing statements

# In[44]:


num = 1/3.
num


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'%e'%num               #scientific notation


# In[46]:


'%4.2f' % num          # float with some specifications


# In[47]:


'{0:4.2f}'.format(num)   #Using format is much better than %


# In[48]:


'%.1f' % 2.567, '{0:.2f}'.format(2.567)


# In[50]:


#More formats

from IPython.display import Image
Image("figures/types.png")


# In[51]:


t = 0.001
y= 10.456


# In[52]:


print 'At t=%g s, the height of the ball is %.2f m.' % (t, y)


# In[53]:


print 'At t={t:g} s, the height of the ball is {y:.2f} m.'.format(
    t=t, y=y)


# # Lists
# mutable objects

# In[54]:


colors = ['red', 'blue', 'green', 'black', 'white']     # no need to define, as in C++


# In[57]:


type(colors)


# In[58]:


lista = [1, 'a', 3, 'hola']           #it can contain a mix of whathever, ..use numpy, more efficient
lista 


# In[59]:


colors[2]     # for i in colors:


# In[60]:


colors[-2]


# In[61]:


# Slice notation
colors[2:4]


# In[62]:


colors[::2]


# In[63]:


# lists are mutable objects


# In[64]:


colors[0] = 'yellow'


# In[65]:


colors


# ### what else I can do?   
#     colors.<TAB>

# In[68]:


colors = ['red', 'blue', 'green', 'black', 'white']    


# In[69]:


colors.append('blue')                                  # in-place


# In[70]:


colors


# In[71]:


colors + ['blue']                                      # it creates a new object


# In[72]:


colors


# ## nested lists

# In[75]:


nest = [1,2,3,[4,5,['target']]]
nest


# In[76]:


nest[3][2][0]


# # Assignment operator
# #Everything is an object

# In[80]:


a = [1, 2, 3]     # Exercise


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b = a


# In[82]:


a


# In[83]:


b


# In[84]:


a is b 


# In[86]:


b[1]= 'hi'               #what's the 'a' value??


# In[87]:


a                         #what happen?? ... asigning, modifies the attributes.


# In[89]:


id(a) == id(b)           #better to make a copy of b, so it doesnt modify


# In[90]:


#python 3 -- old_list.copy()  
# old_list[:]  -- copiar elementos
b = list(a)


# In[91]:


id(b)== id(a)


# ## modify a list  in place
# evitar crear espacios de memoria
# 
# a = [1, 2, 3]
# 
# b= a                  # b point to a
# 
# a.append(4)
# 
# print b

# In[92]:


a = [1, 2, 3]


# In[93]:


id(a)


# In[94]:


a = ['a', 'b', 'c']


# In[100]:


id(a)             # the id changed, cause it created another list


# In[96]:


# siempre no, y me regreso a = [1, 2, 3], id(a)


# In[97]:


a[:] = [1, 2, 3]       


# In[98]:


a


# In[101]:


id(a)             #the id remained, as the list was only modified


# ## back

# In[114]:


colors = ['red', 'blue', 'green', 'black', 'white'] 


# In[115]:


colors.pop()


# In[116]:


colors                              # if wants to remove something it isn't


# In[117]:


colors.remove('green')


# In[118]:


colors


# In[119]:


## adding two colors at the same time? 
colors.append(['blue','purple']) 


# In[120]:


colors


# In[121]:


colors = ['red', 'blue', 'green', 'black', 'white'] 


# In[122]:


colors.extend(['blue', 'purple'])                         #in-place


# In[123]:


colors


# In[124]:


rcolors = colors[::-1]               #assigment
rcolors      


# In[125]:


rcolors2 = list(colors)              #creating a copy 
rcolors2


# In[126]:


rcolors2.reverse()                      #in-place, a method modifies the attributes
rcolors2


# ## sort

# In[127]:


sorted(rcolors)          #new object


# In[128]:


rcolors


# In[129]:


rcolors.sort()           # in-place


# In[130]:


rcolors


# In[131]:


rcolors.count('blue')


# ## random

# In[132]:


import random


# In[133]:


random.random()                   #random numbers within [0,1]


# In[134]:


random.randint(1, 10)


# In[135]:


random.choice(colors)      #chin-chan-pu


# In[136]:


suits = ['hearts', 'clubs', 'diamonds', 'spades']
suits


# In[137]:


random.shuffle(suits)
suits


# # ** Homework 4
# 

# 
# * Dos números amigos son dos números enteros positivos a y b tales que la suma de los divisores propios de uno es igual al otro número y viceversa
# 
#     los divisores propios de 220 son 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 y 110, que suman 284;
#     los divisores propios de 284 son 1, 2, 4, 71 y 142, que suman 220.
#    
# (220, 284), (1184, 1210), (17 296, 18 416) y (9 363 584, 9 437 056)
# 
# * Un número perfecto es un número natural que es igual a la suma de sus divisores propios positivos. Dicho de otra forma, un número perfecto es aquel que es amigo de sí mismo. 
# 
# 28, 496 y 8128
# 
# * Numero abundante σ(x) > 2x.  La suma de todos los divisores positivos de x, incluido el propio x  sumen más que dicho número 24. Sus divisores son 1, 2, 3, 4, 6, 8, 12, 24 cuya suma es 60. Puesto que 60 es mayor que 2×24=48, el número 24 es abundante (sino, deficiente) y su abundancia es σ(x) - 2x (σ(x)= 2x es perfecto)
# 
# 12, 18, 20, 24, 30

# In[30]:


#Esta función permite comprobar si dos números positivos son amigos.


# In[33]:


#Usando la función anterior, comprobamos si un número natural n>1 es perfecto.


# In[57]:


#Esta función nos indica si el número n>1 es deficiente, perfecto o abundante.