Lists

Sequential, Ordered Collection

Creating lists



In [1]:

    
x = [4,2,6,3] #Create a list with values
y = list() # Create an empty list
y = [] #Create an empty list
print(x)
print(y)









    



[4, 2, 6, 3]
[]

Adding items to a list



In [2]:

    
x=list()
print(x)
x.append('One') #Adds 'One' to the back of the empty list
print(x)
x.append('Two') #Adds 'Two' to the back of the list ['One']
print(x)









    



[]
['One']
['One', 'Two']



In [3]:

    
x.insert(0,'Half') #Inserts 'Half' at location 0. Items will shift to make roomw
print(x)









    



['Half', 'One', 'Two']



In [10]:

    
x=list()
x.extend([1,2,3]) #Unpacks the list and adds each item to the back of the list
print(x)
x.extend([4, 5])
print(x)
x.append([7,8])
print(x)









    



[1, 2, 3]
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5, [7, 8]]

Indexing and slicing



In [5]:

    
x=[1,7,2,5,3,5,67,32]
print(len(x))
print(x[3])
print(x[2:5])
print(x[-1])
print(x[::-1])









    



8
5
[2, 5, 3]
32
[32, 67, 5, 3, 5, 2, 7, 1]

Removing items from a list



In [6]:

    
x=[1,7,2,5,3,5,67,32]
x.pop() #Removes the last element from a list
print(x)
x.pop(3) #Removes element at item 3 from a list
print(x)
x.remove(7) #Removes the first 7 from the list
print(x)









    



[1, 7, 2, 5, 3, 5, 67]
[1, 7, 2, 3, 5, 67]
[1, 2, 3, 5, 67]

Anything you want to remove must be in the list or the location must be inside the list



In [7]:

    
x.remove(20)









    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-7-c1262597e831> in <module>()
----> 1 x.remove(20)

ValueError: list.remove(x): x not in list

Mutablility of lists



In [11]:

    
y=['a','b']
x = [1,y,3]
print(x)
print(y)
y[1] = 4
print(y)









    



[1, ['a', 'b'], 3]
['a', 'b']
['a', 4]



In [12]:

    
print(x)









    



[1, ['a', 4], 3]



In [13]:

    
x="Hello"
print(x,id(x))
x+=" You!"
print(x,id(x)) #x is not the same object it was
y=["Hello"]
print(y,id(y))
y+=["You!"] 
print(y,id(y)) #y is still the same object. Lists are mutable. Strings are immutable









    



Hello 4410984912
Hello You! 4411850544
['Hello'] 4410131720
['Hello', 'You!'] 4410131720



In [16]:

    
def eggs(item,total=0):
    total+=item
    return total


def spam(elem,some_list=[]):
    some_list.append(elem)
    print(id(some_list))
    return some_list



In [17]:

    
print(eggs(1))
print(eggs(2))

print(spam(1))
print(spam(2))

Iteration

Range iteration



In [18]:

    
#The for loop creates a new variable (e.g., index below)
#range(len(x)) generates values from 0 to len(x) 
x=[1,7,2,5,3,5,67,32]
for index in range(len(x)):
    print(x[index])



In [19]:

    
list(range(len(x)))
# generator 好处: 节省内存. 如果需要创建一个1billion 的数组, 可以使用这个来创建计数器.









    Out[19]:





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

List element iteration



In [20]:

    
x=[1,7,2,5,3,5,67,32]
for element in x: #The for draws elements - sequentially - from the list x and uses the variable "element" to store values
    print(element)

Practice problem

Write a function search_list that searches a list of tuple pairs and returns the value associated with the first element of the pair



In [39]:

    
def search_list(list_of_tuples,value):
    #Write the function here
    result = 0
    for item in list_of_tuples:
        if item[0] == value:
            return item[1]
    return result



In [40]:

    
prices = [('AAPL',96.43),('IONS',39.28),('GS',159.53)]
ticker = 'IONS'
print(search_list(prices,ticker))
ticker = 'ION'
print(search_list(prices,ticker))

Dictionaries



In [61]:

    
mktcaps = {'AAPL':538.7,'GOOG':68.7,'IONS':4.6}



In [62]:

    
mktcaps['AAPL'] #Returns the value associated with the key "AAPL"









    Out[62]:





538.7



In [63]:

    
mktcaps['GS'] #Error because GS is not in mktcaps









    



---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-63-40312c94d4cd> in <module>()
----> 1 mktcaps['GS'] #Error because GS is not in mktcaps

KeyError: 'GS'



In [64]:

    
mktcaps.get('GS') #Returns None because GS is not in mktcaps



In [65]:

    
mktcaps['GS'] = 88.65 #Adds GS to the dictionary
print(mktcaps)









    



{'GOOG': 68.7, 'GS': 88.65, 'IONS': 4.6, 'AAPL': 538.7}



In [66]:

    
del(mktcaps['GOOG']) #Removes GOOG from mktcaps
print(mktcaps)









    



{'GS': 88.65, 'IONS': 4.6, 'AAPL': 538.7}



In [47]:

    
mktcaps.keys() #Returns all the keys









    Out[47]:





dict_keys(['GS', 'IONS', 'AAPL'])



In [59]:

    
mktcaps.values() #Returns all the values









    Out[59]:





dict_values([88.65, 4.6, 538.7])



In [52]:

    
sorted(mktcaps.keys())









    Out[52]:





['AAPL', 'GS', 'IONS']



In [69]:

    
sorted(mktcaps.values())









    Out[69]:





[4.6, 88.65, 538.7]



In [70]:

    
print(mktcaps)









    



{'GS': 88.65, 'IONS': 4.6, 'AAPL': 538.7}



In [86]:

    
test = {'x':1, 'x':2, 'y':3}



In [87]:

    
test['x']









    Out[87]:





2



In [88]:

    
for item in test:
    print(item[0])

x
y



In [89]:

    
len(test)









    Out[89]:





2

Sets



In [90]:

    
tickers = {"AAPL", "GE", "NFLX", "IONS"}
regions = {"North East", "South", "West coast", "Mid-West"}



In [91]:

    
"AAPL" in tickers









    Out[91]:





True



In [92]:

    
"IBK" in tickers









    Out[92]:





False



In [109]:

    
pharma_tickers = {"IONS", "IMCL"}
tickers.isdisjoint(pharma_tickers) # empty intersection 是否0交集









    Out[109]:





False



In [110]:

    
tickers & pharma_tickers # intersection 交集









    Out[110]:





{'IONS'}



In [111]:

    
tickers | pharma_tickers # union 并集









    Out[111]:





{'AAPL', 'GE', 'IMCL', 'IONS', 'NFLX'}



In [112]:

    
tickers - pharma_tickers # set diference 不同









    Out[112]:





{'AAPL', 'GE', 'NFLX'}



In [113]:

    
tickers > pharma_tickers # superset 是否为父集合









    Out[113]:





False



In [114]:

    
pharma_tickers <= tickers # subset 是否为子集合









    Out[114]:





False



In [115]:

    
pharma_tickers < tickers # proper-subset 是否为子集合









    Out[115]:





False



In [121]:

    
for item in tickers:
    print(item)









    



AAPL
NFLX
IONS
GE



In [126]:

    
s = {1, 2, 4, 3}
s[3] - 4









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-126-e3ade4c98af1> in <module>()
      1 s = {1, 2, 4, 3}
----> 2 s[3]

TypeError: 'set' object does not support indexing



In [122]:

    
dict1 = {"john":40, "peter":45}
dict2 = {"john":466, "peter":45}
dict1 > dict2









    



---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-122-5def35183ff3> in <module>()
      1 dict1 = {"john":40, "peter":45}
      2 dict2 = {"john":466, "peter":45}
----> 3 dict1 > dict2

TypeError: unorderable types: dict() > dict()



In [124]:

    
del dict1["john"]



In [125]:

    
dict1









    Out[125]:





{'peter': 45}



In [ ]: