Python Data Structures

Июль 24, 2022

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Python Data Structures

Содержание

2. Lists An ordered group of items Does not need to be the same type Could put
3. Methods of Lists List.append(x) adds an item to the end of the list List.extend(L) Extend the
4. Examples of other methods a = [66.25, 333, 333, 1, 1234.5] //Defines List print a.count(333), a.count(66.25),
5. Using Lists as Stacks The last element added is the first element retrieved To add an
6. Using Lists as Queues First element added is the first element retrieved To do this collections.deque
7. List Programming Tools Filter(function, sequence) Returns a sequence consisting of the items from the sequence for
8. Map Function Map(function, sequence) Calls function(item) for each of the sequence’s items Computes the cube for
9. Reduce Function Reduce(function, sequence) Returns a single value constructed by calling the binary function (function) Computes
10. The del statement A specific index or range can be deleted
11. Tuples Tuple A number of values separated by commas Immutable Cannot assign values to individual items
12. Sets An unordered collection with no duplicate elements Basket = [‘apple’, ‘orange’, ‘apple’, ‘pear’] Fruit =
13. Dictionaries Indexed by keys This can be any immutable type (strings, numbers…) Tuples can be used
14. Looping Techniques Iteritems(): for retrieving key and values through a dictionary
15. Looping Techniques Enumerate(): for the position index and values in a sequence
16. Zip(): for looping over two or more sequences
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Слайд 2

Lists
An ordered group of items
Does not need to be the same

type
Could put numbers, strings or donkeys in the same list
List notation
A = [1,”This is a list”, c, Donkey(“kong”)]

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Methods of Lists
List.append(x)
adds an item to the end of

the list
List.extend(L)
Extend the list by appending all in the given list L
List.insert(I,x)
Inserts an item at index I
List.remove(x)
Removes the first item from the list whose value is x

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Examples of other methods
a = [66.25, 333, 333, 1, 1234.5] //Defines

List
print a.count(333), a.count(66.25), a.count('x') //calls method
2 1 0 //output
a.index(333)
//Returns the first index where the given value appears
1 //ouput
a.reverse() //Reverses order of list
a //Prints list a
[333, 1234.5, 1, 333, -1, 66.25] //Ouput
a.sort()
a //Prints list a
[-1, 1, 66.25, 333, 333, 1234.5] //Output

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Using Lists as Stacks
The last element added is the first element

retrieved
To add an item to the stack, append() must be used
stack = [3, 4, 5]
stack.append(6)
Stack is now [3, 4, 5, 6]
To retrieve an item from the top of the stack, pop must be used
Stack.pop()
6 is output
Stack is now [3, 4, 5] again

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Using Lists as Queues
First element added is the first element retrieved
To

do this collections.deque must be implemented

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List Programming Tools
Filter(function, sequence)
Returns a sequence consisting of the items from

the sequence for which function(item) is true
Computes primes up to 25

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Map Function
Map(function, sequence)
Calls function(item) for each of the sequence’s items
Computes the

cube for the range of 1 to 11

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Reduce Function
Reduce(function, sequence)
Returns a single value constructed by calling the binary

function (function)
Computes the sum of the numbers 1 to 10

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The del statement
A specific index or range can be deleted

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Tuples
Tuple
A number of values separated by commas
Immutable
Cannot assign values to individual

items of a tuple
However tuples can contain mutable objects such as lists
Single items must be defined using a comma
Singleton = ‘hello’,

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Sets
An unordered collection with no duplicate elements
Basket = [‘apple’, ‘orange’, ‘apple’,

‘pear’]
Fruit = set(basket)
Fruit
Set([‘orange’, ‘apple’, ‘pear’])

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Dictionaries
Indexed by keys
This can be any immutable type (strings, numbers…)
Tuples can

be used if they contain only immutable objects

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Looping Techniques
Iteritems():
for retrieving key and values through a dictionary

Слайд 15

Looping Techniques
Enumerate():
for the position index and values in a sequence

Слайд 16

Python Data Structures

Содержание

ListsAn ordered group of itemsDoes not need to be the same

Methods of ListsList.append(x) adds an item to the end of

Examples of other methodsa = [66.25, 333, 333, 1, 1234.5] //Defines

Using Lists as StacksThe last element added is the first element

Using Lists as QueuesFirst element added is the first element retrievedTo

List Programming ToolsFilter(function, sequence)Returns a sequence consisting of the items from

Map FunctionMap(function, sequence)Calls function(item) for each of the sequence’s itemsComputes the

Reduce FunctionReduce(function, sequence)Returns a single value constructed by calling the binary

The del statementA specific index or range can be deleted

TuplesTupleA number of values separated by commasImmutableCannot assign values to individual

SetsAn unordered collection with no duplicate elementsBasket = [‘apple’, ‘orange’, ‘apple’,

DictionariesIndexed by keysThis can be any immutable type (strings, numbers…)Tuples can

Looping TechniquesIteritems(): for retrieving key and values through a dictionary

Looping TechniquesEnumerate(): for the position index and values in a sequence

Zip(): for looping over two or more sequences

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