1. Variables
Value of the variable is stored in memory
This means that will open up a space in memory when you create a variable
Based on the data type of the variable, the interpreter allocates specified memory, and decide what data can be stored in memory
Thus, the variable can specify different data types, these variables may be stored an integer, decimal, or other characters
2. Assignment
Python does not need to type in the variable assignment statement
Each variable created in memory, including all the variables ID, name and data information
Each variable must be assigned before use variable assignment after the variable will be created
Equal sign (=) is used to assign values to variables
The left side of the equal sign (=) operator is a variable name
The right side of the equal sign (=) operator is the value stored in the variable
counter = 100 # integer variable assignment
Python allows simultaneous assignment to multiple variables
a = b = c = 1
a, b, c = 1, 1.0, "1"
3. Standard
The data stored in memory may be various types
For example, a person's age can be stored digitally, and his name can be used to store characters
Python defines a number of standard types, for storing various types of data.
There are five standard Python data types
Numbers (Digital)
Type for storing the digital data value
Immutable data types
This means changing the numeric data type will be assigned a new object
When you specify a value, Number object is created:
var1 = 1
Del statement can also be used to remove some references to objects
of var1
It supports three different types of numbers:
int (signed integer)
float (float)
complex (plural)
E.g:
int float complex
10 10.0 (10 + 0j)
String (String)
Strings or string (String) is a string of characters consisting of numbers, letters, the underscore
It is the programming language indicates the data type of text
s = "a1a2···an" # (n>=0)
There are two kinds of string list of values in this order:
The default start index 0 from left to right, the maximum range is a little string length
Index of default from right to left at -1, the maximum range is the beginning of a string
s = 'joveH-H'
print (s) # complete output string
print (s [0]) # output of the first character in the string
# joveH-H
# j
If you want to achieve access for a sub-string from a string
You can use [superscript head: Tail index] to intercept the corresponding string
Wherein the subscript is counted from 0, may be positive or negative, the subscript can represent an empty take head or tail
Get a character string containing the subject head, but not the end of the target character
print (s [2: 5]) # string output string between the third to fifth
print (s [2:]) # string output start from the third character
# veH
# veH-H
May receive a third parameter, the parameter is taken action steps
The following examples are for the index to the index 2 and 5 is set to 2 steps (spaced position) to intercept the string
print (s [2: 5: 2]) spacing between string # 2 output string third to fifth
# Articles
List (list)
You can complete the list data structure to achieve most of the collection classes
Support characters, numbers, strings may even contain a list (ie, nested)
List with [] identified python is the most common complex data type
l = ['jove', 10086, 2.23, 'H-H', 20.3]
print(l)
# ['jove', 10086, 2.23, 'H-H', 20.3]
Cutting list values may be used in variable [head superscript: Tail index], the corresponding list will be taken
From left to right index default 0, from right to left index default at -1
Subscripts may take the tail head is empty or represents
The last list element # output print (l [-1])
print (l [1: 3]) # output of the second to the third element
print (l [2:]) # output from the start to the end of the third list of all of the elements
print (l [1: 5: 2]) interval between the elements 2 # output string second to fifth
# 20.3
# [10086, 2.23]
# [2.23, 'H-H', 20.3]
# [10086, 'H-H']
Tuple (tuple)
Tuple is another data type, similar List (list)
Identified by tuple (). Internal element separated by commas
But tuple elements can not be secondary assignment, equivalent to the read-only list
t = ('jove', 10086, 2.23, 'H-H', 20.3)
t [2] = 1000 # tuple is illegal application
# TypeError: 'tuple' object does not support item assignment
Set (collection)
Collection (set) is an unordered sequence of elements will not be repeated
Braces {} may be used or a set () function creates a collection
s1 = {'g', 'o', 'o', 'g', 'l', 'e'}
s2 = { 'g', 'the', 'of', 'g'}
print(s1, s2, s1 - s2)
# { 'And', 'or', 'l', 'g'} { 'or', 'g'} { 'l', 'and'}
Note: Create an empty set must be set () instead of {}, {} as it is used to create an empty dictionary
Dictionary (dictionary)
Dictionary (dictionary) python is in addition to being outside the list of the most flexible type of built-in data structures
List is an ordered collection of objects, dictionaries are unordered collections of objects
The difference between the two is that: among the elements of the dictionary is accessed by a key, rather than by shifting access
Dictionaries with "{}" logo. A dictionary index (key) value and a value corresponding to its composition
d = {'jove': 10086, 2.23: 'H-H'}
print(d[2.23])
print(d.keys())
print(d.values())
# H-H
# dict_keys(['jove', 2.23])
# dict_values([10086, 'H-H'])
4. Conversion
Sometimes the need for built-in data type conversion, simply as a function of the type of data you can name
Several built-in functions can perform conversion between data types
The function returns a new object that represents the converted value
The integer x is converted to a
class int (x, base = 10) # x: string or a number, base: hexadecimal, decimal default
print(int(12.0))
print (int ( "2e", 16)) # but if it is, then base-band parameter, x should be entered as a string
# 12
# 46
The transition to a floating point x
class float ([x]) # x: string or number
print(float(-12))
print(float("20.3"))
# -12.0
# 20.3
Creating a complex
class complex ([real [, imag]]) # real: int, float or string, imag: int, float
print(complex(1, 2))
print(complex("1+2j"))
# (1 + 2j)
# (1 + 2j)
The object is converted to a string x
class str (object = '') # object: Object
str([10, 0, 86])
# '[10, 0, 86]'
The string object is converted to an expression x
class repr (object) # object: Object
repr (str ([10, 0, 86]))
# "'[10, 0, 86]'"
Python expression for calculating effective in the string, and returns an object
class eval(expression[, globals[, locals]])
# Expression: expression
# Globals: variable scope, global namespace, if provided, it must be a dictionary object
# Locals: variable scope, local namespace, if provided, it can be any mapping object
x = 7
print(eval('3 * x'))
# 21 Wuxi flow of the hospital http://xmobile.wxbhnk120.com/
Converting the sequence s is a tuple
class tuple (seq) # seq: tuples to be converted to a sequence of
print(tuple([1, 2, 3]))
# (1, 2, 3)
Converting the sequence s is a list of
class list (tup) # tup: to convert to the list of tuples
print(list((1, 2, 3)))
# [1, 2, 3]
Converted into a set of variable
class set ([iterable]) # iterable: Object iterables
print(set('google'))
# { 'L', 'o', 'g', 'and'}
Create a dictionary
class dict (** kwarg) # ** kwargs: Keyword
Container element: class dict (mapping, ** kwarg) # mapping
class dict (iterable, ** kwarg) # iterable: iterables
# Must be a sequence of (key, value) tuple
print (dict (a = 'a', b = 'b', t = 't')) # incoming keyword
print (dict (zip ([ 'one', 'two', 'three'], [1, 2, 3]))) # mapping function constructed embodiment Dictionary
print (dict ([( 'one', 1), ( 'two', 2), ( 'three', 3)])) # iterables embodiment constructed Dictionary
# {'a': 'a', 'b': 'b', 't': 't'}
# {'one': 1, 'two': 2, 'three': 3}
# {'one': 1, 'two': 2, 'three': 3}
Is converted to a set of immutable
class frozenset ([iterable]) # iterable: objects can be iterative, such as lists, dictionaries, and the like tuple
print(frozenset('google'))
# frozenset({'g', 'l', 'e', 'o'})
If you do not provide any parameters, the default will generate an empty set
Convert an integer to a character
class chr(i) # i：数字
print(chr(48), chr(0x31), chr(0o62))
# 0 1 2
A character into its integer value
class ord (c) # c: Character
print (words ( '6'), words ( 'A'), word ( 'a'))
# 54 65 97
Convert an integer to a hexadecimal string
class hex (x) # x: integer
print(hex(128))
# 0x80
Convert an integer to an octal string
class oct (x) # x: integer
print(oct(1024))
# 0o2000
Thank you!