Python tutorial seventh chapter, data structure

There are three built-in data structures in Python-lists, tuples, and dictionaries.
1) lists list [,]
A list is a sequence of

Shoplist = [' Apple ', ' carrot ', ' banana ']

Print shoplist #[' apple ', ' carrot ', ' banana '

Shoplist.append (' orange ') #末尾加入一个

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

Shoplist.insert (2, ' Flint ') #指定位置插入

Print shoplist #[' apple ', ' carrot ', ' flint ', ' banana ', ' orange '

Shoplist.reverse () #反转

Print shoplist #[' orange ', ' banana ', ' flint ', ' carrot ', ' apple '

Shoplist.pop () #默认从末尾删除

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

Shoplist.sort () #正向排序

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

Del shoplist[1] #指定位置删除, equal to Shoplist.pop (1)

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

Shoplist.extend ([' Database ', ' egg ']) #末尾加入多个

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

Shoplist.remove (' banana ') #删除指定项

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

Get complete knowledge through Help (list).

List parsing expressions
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]

Working with large matrices using open source NumPy systems

Nesting 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]

List parsing

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

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

Index operator
Index operator, subscript operation, starting from 0, supports reverse indexing, 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 '

Slice operator X[i:j]
Slice (slice) operator, with a sequence name followed by square brackets, with a pair of optional digits in square brackets, separated by a colon. The number is optional, and the colon is required.
X[I:J], remove the contents of X from offset to I, until but not including J

>>> 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[1:3] # WA, excluding r!

>>> name[2:] # Aroop

>>> Name[1:-1] # Waroo

>>> name[:] # Swaroop

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

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 ']

If you want to copy a list or a sequence or an object, you must use the slice operator to get the copy. Remember that the assignment statement for the list does not create a copy

Shallow copy deep copy
Shallow copy (1) Full slice operation [:];(2) Use the copy function of the copy module using factory functions such as List (), Dict ();(3)
Deep Copy (1) using the Deepcopy () function of the copy module

Simulating stacks

stack = []

Def pushit ():

    Stack.append (Raw_input ("Enter new String:"). Strip ())

Def popit ():

    If Len (stack) = = 0:

        print ' Can not pops from an empty stack! '

    Else

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

        Stack.pop ()

Def viewstack ():

    Print Stack

CMDs = {' U ':p ushit, ' o ':p opit, ' 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

if __name__ = = ' __main__ ':

2) tuples tuple (,)
Tuples are immutable and cannot be modified. Tuples are defined by a comma-separated list of items 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 use of tuples is in the print statement

Age = 22

name = ' Swaroop '

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

The print statement uses the string of the item tuple followed by the% symbol. The custom output satisfies a particular format. The customization can be%s to represent a string or%d to represent an integer.

3) Dictionaries dictionary {k:v}
Key-value pairs: 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.keys () #[' age ', ' job ', ' name ']

Print rec.values () #[40.5, [' Dev ', ' Mgr ', ' janitor '], {' 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])

Missing Key:

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

>>> value #0

>>> value = d[' x '] if ' x ' in D else 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 a complete list of methods for the Dict class.

4) Set Set ()

A = set (' Abracadabra ')

b = Set (' Alacazam ')

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

Print a # unique letters in a

Print A-B # letters in A and not

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 and not both

Python tutorial seventh chapter, data structure