Python Foundation II

First, the dictionary type

*) dictionary is the only type of mapping in Python, key-value (hash table), the Dictionary object is mutable, but key must be used with immutable objects.

*) dictionary creation and dictionary worthy of access

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# #字典的内容在查看时不能通过索引来进行查看

*) Built-in method: Fromkeys

The key in the dictionary has the same value, the default is None

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*) The dictionary iterates through the access

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*) Addition of Key-value in dictionary

Dic[key] = value

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# #通过字典的添加发现, dictionaries are unordered data types

*) Dictionary deletion

* *) Delete the elements of the dictionary based on the key value

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* *) random deletion of dictionary elements, return (Key,value)

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* *) Delete all elements in the dictionary

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* *) Delete the dictionary itself

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*) Common methods of dictionaries

* *) Dic.get ()

If key exists in the dictionary, the corresponding value value is returned

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* *) Dic.keys ()

Returns all key values in the dictionary

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* *) Update of dictionary content

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* *) Check if a key value exists in the dictionary

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Second, function

*) define Functions

* *) def keyword, which in turn writes out the function name, parentheses, arguments in parentheses, and colons:

* *) write function body in indent block, return value of function returned with return statement.

def fun ():

Pass

Return

*) Call function

Python has built in a lot of useful functions that we can call directly:

* *) sum () # #求和内置函数

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* *) ABS () # #求绝对值

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* *) CMP () # #比较函数

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*) function type conversion

int (obj) # #将字符串转为整型

float (obj) # #转化为浮点型

STR (obj) # #转化为字符串型 *) What is the name of a function

* *) The function name is similar to the variable name, which is actually a reference to a function object;

* *) gives the function an "alias": the function name is assigned to a variable

*) NULL function

Define an empty function that does nothing and can use pass statements;

Pass can be used as a placeholder, and do not think how to write the code of the function, you can put a pass, the entire code first run up

def fun ()

Pass

*) parameter Check

* *) When the function is called, if the number of arguments is incorrect, the Python interpreter will automatically check out and exceed TypeError;

* *) If the parameter type is incorrect, the Python interpreter will not be able to check it for us.

* *) data type checking can be implemented with built-in function isinstance

*) function return value

* *) function return value with return keyword;

* *) returns a tuple that can omit parentheses;

* *) The Python function returns a multivalued value in fact it returns a tuple

* *) When the function is complete without a return statement, auto return None

*) function parameters

* *) when there are multiple parameters, change the large put in front, small changes in the back;

The required parameter is before the default parameter is

*) Variable parameters

Variable parameter is the number of parameters passed in is variable, can be 1, 2 to any, or can be 0

*args

*) keyword Parameters

* *) keyword parameter allows to pass in 0 or any parameter with parameter name;

* *) These keyword parameters are automatically assembled into a dict within the function;

* *) keyword parameter **kwargs

Iii. Advanced features of functions

*) Iteration

This list or tuple can be traversed through a for loop, which we call iteration (iteration)

As long as it is an iterative object, whether there is subscript or not, can iterate, for example, Dict can iterate

*) How to tell if an object can iterate

Judging by the iterable type of the collection module

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*) using Python's built-in enumeration method, enumerate a list into an index-element pair

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*) for loop, referencing two variables at the same time, and iterating over the display

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*) List-generated

Range Module

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List-generation:

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# #循环太麻烦, and list generation can use a single line of statements instead of loops to generate the above list

*) List Builder

* *) Why List Builder is required:

Through the list generation, we can directly create a list, subject to memory constraints, the list capacity is certainly limited;

Create a list of 1 million elements that occupy a large amount of storage space;

* *) What the generator is:
The subsequent elements are continually extrapolated during the loop, so that you do not have to create a complete list, which saves a lot of space. In Python, this side loop is calculated as a mechanism, called the generator

# #使用g. Next () method reads the element sequentially (troublesome)

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# #使用for循环 (Quick and easy)

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Python Foundation II