Lists

Some methods of list:

list.append(x): add x to the end
list.insert(i, x): insert x at position i
list.index(x): return index of the first item whose value is x
list.pop([i]): remove item at position i. default value is 0



In [29]:

    
pets = ['dog', 'cat', 'pig']
print pets.index('cat')



In [30]:

    
pets.insert(0, 'rabbit')
print pets









    



['rabbit', 'dog', 'cat', 'pig']



In [31]:

    
pets.pop(1)
print pets









    



['rabbit', 'cat', 'pig']

del statement can be used to remove an item from a list given its index



In [3]:

    
a = range(10)
print a









    



[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]



In [6]:

    
del a[2]
print a









    



[0, 1, 3, 4, 5, 6, 7, 8, 9]



In [5]:

    
print a[:3]









    



[0, 1, 2]



In [7]:

    
del a[:3]
print a









    



[4, 5, 6, 7, 8, 9]

list(): convert a sequence to a list



In [76]:

    
print list('i can eat glass')









    



['i', ' ', 'c', 'a', 'n', ' ', 'e', 'a', 't', ' ', 'g', 'l', 'a', 's', 's']

Sort a list

sorted(list, [cmp=None[, key=None[, reverse]]]): return a new sorted list
list.sort([cmp=None[, key=None[, reverse]]]): sort the current list (not creating new list)

where:

cmp: custom comparison function should return a negative, zero or positive number depending on whether the first argument is considered smaller than, equal to, or larger than the second argument
key: function extracting a comparison key from each list element.
reverse: if True, ascending sort otherwise, descending sort.



In [73]:

    
print sorted([2, 3, 1], reverse=True)
a = [2, 3, 1]
print a.sort(reverse=True)
print a









    



[3, 2, 1]
None
[3, 2, 1]



In [74]:

    
print sorted([
    ['peter', 23],
    ['john', 30],
    ['tom', 18]
], key=lambda x: x[1])









    



[['tom', 18], ['peter', 23], ['john', 30]]

List comprehensive

a concise way to create list
when need to create a list... think about it



In [38]:

    
squares = []
for x in range(10):
    squares.append(x**2)
print squares









    



[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]



In [14]:

    
print [x**2 for x in range(10)]









    



[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]



In [11]:

    
array = []
for x in [1,2,3]:
    for y in [1, 2, 3]:
        if x != y:
            array.append((x, y))
print array









    



[(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]



In [12]:

    
print [(x, y) for x in [1,2,3] for y in [1,2,3] if x != y]









    



[(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]

Tuples

lists and strings are two examples of sequence data types.
tuple can think like list, but it is immutable.
- Note: no tuple comprehensive



In [16]:

    
t = (1, 2, 3, 4, 5)
print t









    



(1, 2, 3, 4, 5)



In [21]:

    
tuple([1,2,3])









    Out[21]:





(1, 2, 3)



In [43]:

    
# change the tuple raise exception
t[0] = 5









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-43-db18f5e48428> in <module>()
      1 # change the tuple raise exception
----> 2 t[0] = 5

TypeError: 'tuple' object does not support item assignment

Sets

A set is an unordered collection with no duplicate elements
Curly brackets can use to create set, but {} create dictionary instead of set
set(): convert a sequence to a set



In [22]:

    
letters = {'a', 'b', 'c', 'a'}
print letters









    



set(['a', 'c', 'b'])



In [23]:

    
print set(['a', 'b', 'c', 'a'])









    



set(['a', 'c', 'b'])



In [23]:

    
s = set(['a', 'b'])
s.add('c')

print s









    



set(['a', 'c', 'b'])

add item to a set



In [104]:

    
pets = { 'dog', 'cat', 'pig' }
pets.add('dog')
print pets
pets.add('fish')
print pets









    



set(['cat', 'dog', 'pig'])
set(['fish', 'cat', 'dog', 'pig'])

check item is in a set



In [105]:

    
print 'fish' in pets
print 'lion' in pets









    



True
False

delete item



In [106]:

    
pets.remove('fish')
print pets









    



set(['cat', 'dog', 'pig'])

similarly to list comprehensions, set comprehensions are also supported



In [24]:

    
letters = {x for x in 'i can eat glass'}
print letters









    



set(['a', ' ', 'c', 'e', 'g', 'i', 'l', 'n', 's', 't'])

you can loop over the set



In [75]:

    
for c in set('i can eat glass'):
    print c,









    



a   c e g i l n s t

Dictionaries

it's mapping type: key -> value
key can be any immutable type: usually string or number



In [ ]:

    
{'a', 'b'}



In [26]:

    
tel = {'jack': 4098, 'sape': 4139}
tel['guido'] = 4127

print tel









    



{'sape': 4139, 'jack': 4098, 'guido': 4127}



In [27]:

    
tel['vu'] = 4910



In [28]:

    
print tel









    



{'vu': 4910, 'sape': 4139, 'jack': 4098, 'guido': 4127}



In [26]:

    
print tel['jack']

delete key in dictionary



In [92]:

    
del tel['guido']
print tel









    



{'sape': 4139, 'jack': 4098}

check if a key is in dictionary



In [29]:

    
print 'sape' in tel
print 'foo' in tel









    



True
False

dict.keys(): return list of keys
dict.values(): return list of values



In [30]:

    
tel = {'sape': 4139, 'jack': 4098, 'guido': 4127}

print tel.keys()
print tel.values()









    



['sape', 'jack', 'guido']
[4139, 4098, 4127]

dictionary can be construct by calling
- dict(sequence): where a sequence of (key, value) pairs



In [31]:

    
print dict([('sape', 4139), ('jack', 4098), ('guido', 4127)])









    



{'sape': 4139, 'jack': 4098, 'guido': 4127}

zip(sequence...): zip sequences together



In [115]:

    
zip([1, 2, 3], 'abc', 'ABC')









    Out[115]:





[(1, 'a', 'A'), (2, 'b', 'B'), (3, 'c', 'C')]



In [116]:

    
print dict(zip('abc', [1, 2, 3]))









    



{'a': 1, 'c': 3, 'b': 2}

Loop over a dictionary



In [83]:

    
for name in tel:
    print name, ':', tel[name]









    



sape : 4139
jack : 4098
guido : 4127



In [32]:

    
tel.values()









    Out[32]:





[4139, 4098, 4127]



In [81]:

    
for telno in tel.values():
    print telno

Generator & iterator

Generator

generator: for lazy (on demand) generating of sequence of values
performance benefit!



In [34]:

    
def firstn(n):
    i = 0
    while i < n:
        yield i
        i += 1



In [35]:

    
gen = firstn(10)



In [42]:

    
print range(50)
print firstn(50)









    



[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49]
<generator object firstn at 0x10adad2d0>



In [58]:

    
for i in range(5):
    print i,
    
print '\n--------------------'

for i in firstn(5):
    print i,









    



0 1 2 3 4 
--------------------
0 1 2 3 4

comprehensive syntax like list comprehensive



In [62]:

    
for i in (x ** 2 for x in range(10)):
    print i,









    



0 1 4 9 16 25 36 49 64 81

Iterator

iterator: is an object that enables a program to traverse though a sequence
for statement: loop through any iterator



In [45]:

    
for i in xrange(10):
    print i,









    



0 1 2 3 4 5 6 7 8 9

More on looping

enumerate(sequence, start=0)



In [47]:

    
list(enumerate(['dog', 'cat', 'pig']))









    Out[47]:





[(0, 'dog'), (1, 'cat'), (2, 'pig')]



In [89]:

    
print list(enumerate(['dog', 'cat', 'pig']))
print list(enumerate(['dog', 'cat', 'pig'], start=2))









    



[(0, 'dog'), (1, 'cat'), (2, 'pig')]
[(2, 'dog'), (3, 'cat'), (4, 'pig')]



In [48]:

    
for value in enumerate(['dog', 'cat', 'pig']):
    print value









    



(0, 'dog')
(1, 'cat')
(2, 'pig')



In [91]:

    
for index, value in enumerate(['dog', 'cat', 'pig']):
    print index, ':', value









    



0 : dog
1 : cat
2 : pig

dict.iteritems(): return an iterator through items (key, value) of a dictionary
dict.iterkeys(): return an iterator through key of a dictionary
dict.itervalues(): return an iterator through value of a dictionary



In [52]:

    
print tel









    



{'sape': 4139, 'jack': 4098, 'guido': 4127}



In [53]:

    
print list(tel.iteritems())









    



[('sape', 4139), ('jack', 4098), ('guido', 4127)]



In [54]:

    
for name, telno in tel.iteritems():
    print name, ':', telno









    



sape : 4139
jack : 4098
guido : 4127



In [56]:

    
for key in tel.iterkeys():
    print key









    



sape
jack
guido



In [57]:

    
import os



In [65]:

    
os.listdir('.')









    Out[65]:





['.DS_Store',
 '.git',
 '.gitignore',
 '.ipynb_checkpoints',
 '0.0_Introduction.ipynb',
 '0.0_Introduction.slides.html',
 '1.0_Control_Flows.html',
 '1.0_Control_Flows.ipynb',
 '1.0_Control_Flows.slides.html',
 '2.0_Functions.ipynb',
 '2.0_Functions.slides.html',
 '3.0_Data_structures.ipynb',
 '3.0_Data_structures.slides.html',
 '4.0_Modules.ipynb',
 '4.0_Modules.slides.html',
 '5.0_Practices.ipynb',
 'assets',
 'examples',
 'LICENSE',
 'main.py',
 'module_a.py',
 'module_b.py',
 'README.md']



In [59]:

    
[file_name for file_name in os.listdir('.') if file_name.endswith('.pyc')]









    Out[59]:





['main.pyc', 'module_a.pyc', 'module_b.pyc']



In [64]:

    
filter(lambda file_name: file_name.endswith('.pyc'), os.listdir('.'))









    Out[64]:





[]



In [61]:

    
os.remove('./main.pyc')



In [63]:

    
[os.remove(file_name) for file_name in os.listdir('.') if file_name.endswith('.pyc')]









    Out[63]:





[None, None]



In [ ]: