Python Learning Note 3: Collections, file operations, functions

A. Collection

1.

>>> S=set ([1,2,3,4,5,6,6,6,])
>>> s
{1, 2, 3, 4, 5, 6}

A collection can be understood as a dictionary with keys that have no value, and the keys are de-weighed and unordered.

2. Set Operation:

>>> s1={1,2,3,4,5,6,7}
>>> s2={6,7,8,9,10,11}
>>> S1&S2
{6, 7}//intersection
>>> S1|S2
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}//
>>> S1^S2
{1, 2, 3, 4, 5, 8, 9, 10, 11}//difference set

3. Adding and removing elements

>>> S=set ([1,2,3,4,5,5,5,8])
>>> s
{1, 2, 3, 4, 5, 8}
>>> s.add (' Hello ')
>>> s
{1, 2, 3, 4, 5, ' Hello ', 8}
>>> S.remove (5)
>>> s
{1, 2, 3, 4, ' Hello ', 8}

Two. File operation

1.open function Open File mode:

(1) r, read-only mode

(2) W, write-only mode: unreadable, nonexistent, create, delete content

(3) A, append mode: Readable, non-existent then created, only append content exists

+ identity can write a file at the same time

2. Close the file:

(1) Close function

(2) with:

>>> with open ("/root/1.txt", "R") as F:
... f.readlines ()
...
[' This was a txt file line1\n ', ' This is a txt file line2\n ']

3. File iterators

1. How to use:

>>> with open ("/root/1.txt", "R") as F:
... f.readlines ()
...
[' This was a txt file line1\n ', ' This is a txt file line2\n ']
>>> with open ("/root/1.txt", "R") as F:
... for line in F:
.. print (line)
...
This is a TXT file line1

This is a TXT file line2

Benefit: Avoid the ReadLines method to read the file into memory at once

Three. Functions

1. Definition: A function refers to the collection of a set of statements by a name to encapsulate, to execute this function, simply call its function name to

2. Features:

Reduce duplication of code, make programs extensible, and make programs easier to maintain

3. Scope: A variable within a function does not affect the value of a variable defined by a function sibling, and needs to be changed to use the global declaration within a function

4. Position parameters and keyword parameters

A. Keyword parameter cannot precede position parameter

B.*args:

>>> def Fun (*args):
.. print (*args)
...
>>> Fun ("Hello World", +)
Hello World 1 2

Accept arbitrary multi-position parameters

C.**args:

>>> def Fun (X,y,z=1,*args,**kwargs):
... print (x, y, z)
.. print (args)
.. print (Kwargs)
...
>>> Fun (1,2,3,4,5,6,foo= "Hello python!")
1 2 3
(4, 5, 6)
{' foo ': ' Hello python! '}
>>> Fun (+)
1 2 1
()
{}

Python Learning Note 3: Collections, file operations, functions