# The core data types of Python learning

Source: Internet
Author: User

Python Core data types

Object Type Example

Digital 1234,-345

String ' spam '

list [1,3, ' DS ']

Tuples (1, ' spam ', 6)

Dictionary {' name ': ' Lili ', ' Age ': 12}

File myfile =open (' Test.text ', ' W)

Set set (' ABC ')

Other Types None Boolean type

Programming unit type functions, modules, classes

Digital

Add, subtract, multiply, divide, needless to say, +-*/

* * indicates that the exponentiation 2**3 represents 2 of the three-square result is 8

>>>2**100

1267650600228229401496703205376L

Will find that even a large number, Python can be output correctly, the result may be saved with a string,

In addition to expressions, there are some common math modules that are distributed with Python, which are just the extra toolkits we import for use
Import Math
>>>math.pi

Import Random
>>>random.random ();
string
In Python we can also reverse the index, starting with the last
s = "Dhsaj"
&GT;&GT;&GT;S[-1]
J
>>>s[-2]
A
In addition to a simple positional index, the sequence supports a so-called Shard operation. This is a one-step way to implement the entire Shard
s = "spam"
>>>s[1:3]
Pa
>>>s[1:] All sequences starting with ordinal 1
Pam
>>>s
Spam
>>>s[0:3]
Spa
>>>s[:3] From the beginning to the sequence preceded by the ordinal 3
Spa
&GT;&GT;&GT;S[:-1] The sequence from the beginning to the last
Spa
>>>s[:] From the beginning to the last sequence
Spam

Strings are also supported for merging by adding good
s = "spam" + "name"
>>>s
Spamname
>>>s*2 repeat two times
Spamnamespamname

Non-denaturing
Python strings cannot be changed after they are created
s = "spam"
>>>s[0] = ' Z '
Error
s = ' Z ' +s[1:];
>>>s
Zpam

Type-specific methods
Find can do a string lookup
Replace will search and replace the global
s = "spam"
>>>s.find ("Pa");
1
>>>s.replace ("Pa", "XYZ");
Sxyzpam
>>>s
Spam

Although the names of these string methods are changed by meaning, but here we do not change the original string, but instead will create a new string as the result, because the string has immutability

line = "AAA,BBB,CCC,DDD";
>>>line.split (', '); Splitting a string into a city a list of strings
[' AAA ', ' BBB ', ' CCC ', ' DDD ']
s = ' spam '
>>>s.upper () Change case
SPAM
>>>s.isalpha () test string contents
True
line = ' aaa,bbb,ccc\n ';
>>>line = Line.rstrip () Removes the space character from the right
>>>line
' AAA,BBB,CCC '

The string also supports a high-level substitution operation called formatting,
>>> '%s,eggs,and%s '% (' spam ', ' spam ')
' Spam,eggs,and,spam '

>>> ' {0},eggs,and{1} '. Format (' spam ', ' spam ')
' Spam,eggs,and,spam '

The previous section of the method is representative, but only a few examples of strings, you can call the built-in Dir function, will return a list, including all the properties of the object,

>>>dir (s)
[' __add__ ', ' __class__ ', ' __contains__ ', ' __delattr__ ', ' __doc__ ', ' __eq__ ', ' __format__ ', ' __ge__ ', ' __getattribute__ ' ', ' __getitem__ ', ' __getnewargs__ ', ' __getslice__ ', ' __gt__ ', ' __hash__ ', ' __init__ ', ' __le__ ', ' __len__ ', ' __lt__ ' , ' __mod__ ', ' __mul__ ', ' __ne__ ', ' __new__ ', ' __reduce__ ', ' __reduce_ex__ ', ' __repr__ ', ' __rmod__ ', ' __rmul__ ', ' __setat ' Tr__ ', ' __sizeof__ ', ' __str__ ', ' __subclasshook__ ', ' _formatter_field_name_split ', ' _formatter_parser ', ' capitalize ' , ' center ', ' count ', ' decode ', ' encode ', ' endswith ', ' expandtabs ', ' find ', ' format ', ' Index ', ' isalnum ', ' isalpha ', ' ISD Igit ', ' islower ', ' isspace ', ' istitle ', ' isupper ', ' join ', ' ljust ', ' lower ', ' lstrip ', ' partition ', ' replace ', ' rfind ' , ' Rindex ', ' rjust ', ' rpartition ', ' rsplit ', ' Rstrip ', ' Split ', ' splitlines ', ' startswith ', ' strip ', ' swapcase ', ' title ', ' Translate ', ' upper ', ' Zfill ']

The Dir function simply gives the name of the method, to query what they do, can pass parameters to the Help function
>>>help (' SSS '. Replace)
Help on built-in function replace:

Replace (...)
S.replace (old, new[, Count]), string

Return a copy of string S with all occurrences of substring
Old replaced by new. If The optional argument count is
Given, only the first count occurrences is replaced.

List
Python lists are not like the C language that requires a uniform type, Python lists can hold different types
Because the list is mutable, most of the list's methods will change the list object in place, rather than creating a new list

L = [N, "Das", 34];
>>>len (L)
3
&GT;&GT;&GT;L[0]
12
&GT;&GT;&GT;L[:-1]
"Das"
>>>l+[4,5,6]
["Das", 34,4,5,6]
>>>l.append (' AA ');
[' Das ', ' AA ']
>>>l.pop (2)
[A, ' Das ', AA]
>>>l.sort () sort
>>>l.reverse (); Flip
The list does not have a fixed size, but it still makes it impossible to access data beyond the end of the footer
------------------------------------------------------------
Nesting
Python can support arbitrary nested forms
Is that you can nest another list or even a single ancestor in one list.
---------------------------------------------------------------
List parsing

m=[[+],
[4,5,6],
[7,8,9]
];
>>>cols = [row[1] for row in M]; Remove the second column from M the row corresponds to each list element in M
>>>cols
[2,5,8]
>>> cols = [row[1] for row in m if row[1]%2 = = 0] Also support judgment statement
[2,8]
>>> double = [c*2 for C in "spam"];
>>>double
[' SS ', ' pp ', ' AA ', ' mm '];

Dictionary

A dictionary is not a sequence, but a mapping that is stored by a key rather than a relative position, but simply by mapping the key to a value

>>>d = {' food ': ' spam ', ' Color ': 4}
>>>d[' food ']
' Spam '
>>>d = {' name ': {' last ': Smith, ' first ': ' Bob '},
' Age ': 23,
' Job ': ' AA '}
>>>d[' name ']
{' Last ': Smith, ' first ': ' Bob '},
>>>d[' name ' [' first ']
' Bob '
>>>d = {' A ': 1, ' C ': 2, ' B ': 3}
>>> li = List (D.keys ())
>>>li
[' A ', ' C ', ' B ']
>>> Li.sort ();
>>> Li
[' A ', ' B ', ' C '];

Meta-group
is basically an immutable list.

>>> t = (1,2,3,4)
>>>len (t)
4
>>>t + (5,6);
(1,2,3,4,5,6)
In 3.0 by two proprietary methods
T.index (4)
3
T.count (3)
1
also supports mixed types and nesting, but not growth or shortening,

file
To create a file object, you need to call the built-in function, and an operation mode,

>>>f = open (' File1.txt ', ' W ')
>>>f.wirte (' hello\n ')
>>>f.write (' world\n ')
>>>f.close ();

>>>f = open (' File1.txt ', ' R ') R RB
>>>f.close ()
>>>str
>>

----------------------------------
>>> L = [1,2,3,4]
>>> Type (l)
<type list>
>>> type (Type (l))
<type Type>
The following three types are used to determine the type of
if (type (l) = = Type ([])) {
}
if (type (l) = = list) {
}
if (Isinstance (l,list)) {
}
------------------------------ ----------------------------------------------
user-defined class

Class student:
def  __init__ (self,name):
self.name = name;
def  GetName (self):
return self.name;
def setName (self,name):
self.name = name;

STU1 = student (' Lil ');
name = Stu1.getname ();
Print (name);

Stu1.setname (' aaa ');
Name = Stu1.getname ();
Print (name);

Python learning core data types

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