Python tutorial chapter 7, data structure, python Chapter 7

Python tutorial chapter 7, data structure, python Chapter 7

Python has three built-in data structures: List, tuples, and dictionary.
1) Lists List [,]
A list is a sequence.

shoplist = ['apple', 'carrot', 'banana']

print shoplist #['apple', 'carrot', 'banana']

Shoplist. append ('Orange ') # Add

print shoplist #['apple', 'carrot', 'banana', 'orange']

Shoplist. insert (2, 'flint') # insert at the specified position

print shoplist #['apple', 'carrot', 'flint', 'banana', 'orange']

Shoplist. reverse () # reverse

print shoplist #['orange', 'banana', 'flint', 'carrot', 'apple']

Shoplist. pop () # delete from the end by default

print shoplist #['orange', 'banana', 'flint', 'carrot']

Shoplist. sort () # forward sorting

print shoplist #['banana', 'carrot', 'flint', 'orange']

Del shoplist [1] # delete at the specified position, which is equal to shoplist. pop (1)

print shoplist #['banana', 'flint', 'orange']

Shoplist. extend (['database', 'egg']) # add multiple

print shoplist #['banana', 'flint', 'orange', 'database', 'egg']

Shoplist. remove ('banana ') # delete a specified item

print shoplist #['flint', 'orange', 'database', 'egg']

Use help (list) to obtain complete knowledge.

List parsing expression
Export a new list from an existing list.

vec = [2, 4, 6]

print (3 * x for x in vec) #<generator object <genexpr> at 0x00E7D300>

print list(3 * x for x in vec) #[6, 12, 18]

print [3 * x for x in vec] # [6, 12, 18]

print [3 * x for x in vec if x > 3] # [12, 18]

print [3 * x for x in vec if x < 2] # []

print [[x, x**2] for x in vec] # [[2, 4], [4, 16], [6, 36]]

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

print [row[1] for row in M] # [2, 5, 8]

print [row[1] for row in M if row[1] % 2 == 0] #[2, 8] 

print [x + y for x in 'abc' for y in 'mn'] #['am', 'an', 'bm', 'bn', 'cm', 'cn'] 

Use the open-source NumPy system to process large Matrices

Nesting

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

print M #[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

print M[0] #[1, 2, 3]

print M[1][2] #6 

List Parsing

>>> list(map(sum, M)) #[6, 15, 24]

>>> {sum(row) for row in M} #set([24, 6, 15])

>>> {x: ord(x) for x in 'spabm'} #{'a': 97, 'p': 112, 's': 115, 'b': 98, 'm': 109} 

Index Operator
Index operator, subscript operation, starting from 0, supports reverse index, starting from-1

>>> sp = ['a', 'b', 'c', 'd']

>>> sp[0], sp[1], sp[2], sp[3] #('a', 'b', 'c', 'd')

>>> sp[-4], sp[-3], sp[-2], sp[-1] #('a', 'b', 'c', 'd')

>>> name = 'swaroop'

>>> len(name) #7

>>> name[-1] #'p'

>>> name[len(name) - 1] #'p' 

Slice operator X [I: J]
Slice operator, sequence name and square brackets, which contain an optional number and are separated by a colon. Numbers are optional, while colons are required.
X [I: J], which is taken from offset to I in X until the content of J is not included.

>>> shoplist = ['a', 'b', 'c', 'd']

>>> shoplist[1:3] #['b', 'c']

>>> shoplist[2:] #['c', 'd']

>>> shoplist[1:-1] #['b', 'c']

>>> shoplist[:] #['a', 'b', 'c', 'd']

name = 'swaroop'

>>> Name [] # wa, excluding r!

>>> name[2:] # aroop

>>> name[1:-1] # waroo

>>> name[:] # swaroop

>>> name * 2 # swaroopswaroop 

Ternary slice operator X [I: J: K]

X[I:J] = X[I:J:1]

s = "abcdefghijklmn"

print s[1:10:2] #bdfhj

print s[::2] #acegikm

print s[::-2] #nljhfdb 

Reference

shoplist = ['apple', 'mango', 'carrot', 'banana']

mylist = shoplist # mylist is just another name pointing to the same object!

del shoplist[0]

print shoplist # ['mango', 'carrot', 'banana']

print mylist # ['mango', 'carrot', 'banana']

mylist = shoplist[:] # make a copy by doing a full slice

del mylist[0] # remove first item

print shoplist # ['mango', 'carrot', 'banana']

print mylist # ['carrot', 'banana']

To copy a list, sequence, or object, you must use the slice operator to copy the object. Remember that the assignment statement of the list is not copied.

Deep copy
Shallow copy (1) Complete slicing operation [:]; (2) use factory functions, such as list () and dict (); (3) use the copy function of the copy Module
Deep copy (1) Use the deepcopy () function of the copy Module

Simulate Stack

stack = []

def pushit():

    stack.append(raw_input("Enter new String:").strip())

def popit():

    if len(stack) == 0:

        print 'Can not pop from an empty stack!'

    else:

        print 'Removed [', stack[-1], ']'

        stack.pop()

def viewstack():

    print stack

CMDs = {'u':pushit, 'o':popit, 'v':viewstack}

def showmenu():

    pr = """p(U)sh  p(O)p (V)iew (Q)uit  Enter choice:"""

    while True:

        while True:

            try:

                choice = raw_input(pr).strip()[0].lower()

            except (EOFError, KeyboardInterrupt, IndexError):

                choice = 'q'

            print '\nYou picked: [%s]' %choice

            if choice not in 'uovq':

                print 'Invalid option, try again'

            else:

                break

        if choice == 'q':

            break

        CMDs[choice]() 

if __name__ == '__main__':

showmenu() 

2) Tuples (,)
Tuples are unchangeable and cannot be modified. The tuples are defined by commas (,) in parentheses.

zoo = ('w', 'e', 'p')

new_zoo = ('m', 'd', zoo)

print zoo #('w', 'e', 'p')

print new_zoo #('m', 'd', ('w', 'e', 'p'))

print new_zoo[2] #('w', 'e', 'p')

print new_zoo[2][2] #p

new_zoo[1] = 'x' #TypeError: 'tuple' object does not support item assignment

The most common usage of tuples is to use them in print statements.

age = 22

name = 'Swaroop'

print '%s is %d years old' % (name, age)

print 'Why is %s playing with that python?' % name 

The print statement uses a string of the Project tuples followed by the % symbol. Custom output meets a specific format. The Value % s indicates a string or % d indicates an integer.

3) Dictionaries dictionary {k: v}
Key-Value Pair: d = {key1: value1, key2: value2}

rec = {'name': {'first': 'Bob', 'last': 'Smith'}, 'job': ['dev', 'mgr'], 'age': 40.5}

print rec['name'] #{'last': 'Smith', 'first': 'Bob'}

print rec['name']['last'] #'Smith'

print rec['job'] #['dev', 'mgr']

print rec['job'][-1] #'mgr'

rec['job'].append('janitor')

print rec #{'age': 40.5, 'job': ['dev', 'mgr', 'janitor'], 'name': {'last': 'Smith', 'first': 'Bob'}} 

print rec.keys() #['age', 'job', 'name']

print rec.values() #[40.5, ['dev', 'mgr', 'janitor'], {'last': 'Smith', 'first': 'Bob'}]

print rec.items() #[('age', 40.5), ('job', ['dev', 'mgr', 'janitor']), ('name', {'last': 'Smith', 'first': 'Bob'})] 

Sorting Key:

>>> D = {'a': 1, 'b': 2, 'c': 3}

>>> sorted(D) #['a', 'b', 'c']

D = {'a': 1, 'c': 3, 'b': 4}

for k in sorted(D.keys()): print(k, D[k])

for k in sorted(D): print(k, D[k]) #('a', 1) ('b', 4) ('c', 3) 

Missing Key:

>>> value = D.get('x', 0)               

>>> value #0

>>> value = D['x'] if 'x' in D else 0   

>>> value #0 

Other Ways

d = dict(zip(['a', 'b', 'c'], [1, 2, 3]))

print d # {'a': 1, 'c': 3, 'b': 2}

D = {c: c * 4 for c in 'SPA'}

print D #{'A': 'AAAA', 'P': 'PPPP', 'S': 'SSSS'}

Use help (dict) to view the complete list of dict classes.

4) set ()

a = set('abracadabra')

b = set('alacazam')

Y = {'h', 'a', 'm'} #python3

print a # unique letters in a

print a - b # letters in a but not in b

print a | b # letters in either a or b

print a & b # letters in both a and b

print a ^ b # letters in a or b but not both