Detailed description of Python variables and data types

python variables and data types

One, integer

int = 20print Intprint 45678 + 0x12fd2

Second, floating point number

float = 2.3print float

Three, string

A, use single quotation marks (') to enclose the string in single quotation marks, for example: str = ' This is string ' Print strb, use double quotation marks (") in double quotation marks and string usages in single quotes exactly the same, for example: str =" This is a string "; Print STRC, using three quotation marks ("") to represent multiple lines of string, can be used to freely use single and double quotation marks in three quotation marks, for example: str = "This is Stringthis is Pythod stringthis is a string" Print str

Four, Boolean value

And: With operations, only the result of all true,and operations is true. Or: Or operation, as long as one of the true,or operation results is true. Not: Non-arithmetic, which is a monocular operator that turns true into False,false to true. bool = Falseprint Boolbool = trueprint bool

Five, null value

The null value is a special value in Python, denoted by none. None cannot be understood as 0, because 0 is meaningful, and none is a special null value.

Vi. List

#-*-Coding:utf-8-*-lst = [' A ', ' B ', 1996, 2017]nums = [1, 3, 5, 7, 8, 13, 20]# the value in the Access list print "nums[0]:", Nums[0] # 1PRI  NT "Nums[2:5]:", Nums[2:5] # [5, 7, 8]print "Nums[1:]:", Nums[1:] # [3, 5, 7, 8,, 20]print "nums[:-3]:", nums[:-3] # [1, 3, 5, 7]print "nums[:]:", nums[:] # [1, 3, 5, 7, 8, 13, 20]# update list nums[0] = "LJQ" Print nums[0]# delete list element del nums[0] "n ums[:]: [3, 5, 7, 8, +] "print" nums[:]: ", nums[:]# list script operator print len ([1, 2, 3]) # 3print [1, 2, 3] + [4, 5, 6] # [ 1, 2, 3, 4, 5, 6]print [' hi! '] * 4 # [' hi! ', ' hi! ', ' hi! ', ' hi! '] Print 3 in [1, 2, 3] # truefor x in [1, 2, 3]: Print x, # 1 2 3# list intercept L = [' spam ', ' spam ', ' spam! '] Print l[2] # ' spam! ' Print L[-2] # ' Spam ' Print l[1:] # [' Spam ', ' spam! '] # List Function & method Lst.append (' Append ') # Add a new object at the end of the list Lst.insert (2, ' Insert ') # Inserts an object into the list Lst.remove (1996) # Removes the first occurrence of a value in the list LST. Reverse () # Reverse List of elements, reverse print lst.sort () # sort the original list print Lst.pop (1) # removes an element from the list (the last element by default), and returns the value of the element print Lstprint lst.co Unt (' obj ') # statistic an element appears in the listNumber of times Lst.index (' append ') # Find the index position of the first occurrence of a value from the list, index starting at 0 lst.extend (LST) # Append multiple values from another sequence at the end of the list (the original list is expanded with a new list) print ' End: ' Lst

Seven, the dictionary

The Dictionary (dictionary) is the most flexible built-in data structure type in Python, in addition to the list. A list is an ordered combination of objects, and a dictionary is a collection of unordered objects. The difference between the two is that the elements in the dictionary are accessed by keys, not by offsets.

#-*-Coding:utf-8-*-dit = {' name ': ' Zara ', ' age ': 7, ' class ': ' first '}dict1 = {' abc ': 456}DICT2 = {' abc ': 123, 98.6:37} Seq = (' name ', ' age ', ' sex ') # access the value in the dictionary print "dit[' name ']:", dit[' name ']print "dit[' age ':", dit[' age ']# Modify dictionary dit["age"] =  27 # Modify the value of the existing key dit["school"] = "Wutong" # Add a new key/value pair to print "dict[' Age '": ", dit[' age ']print" dict[' School ']: ", dit[' school ']# Delete Dictionary del dit[' name ' # Delete key is ' name ' entry dit.clear () # Empty dictionary all entries del dit # Delete dictionary dit = {' name ': ' Zara ', ' age ': 7, ' class ': ' Firs T '}# dictionary built-in Functions & Methods CMP (Dict1, DICT2) # compare two dictionary elements. Len (DIT) # computes the number of dictionary elements, that is, the total number of keys. The Str (DIT) # Output dictionary is a printable string representation. Type (DIT) # Returns the type of the variable entered and returns the dictionary type if the variable is a dictionary. Dit.copy () # Returns a shallow copy of a dictionary dit.fromkeys (seq) # Creates a new dictionary with the keys of the elements in the sequence seq, Val is the initial value corresponding to the dictionary for all Keys Dit.get (dit[' name ']) # Returns the value of the specified key, If the value does not return the default value in the Dictionary Dit.has_key (' class ') # If the key returns true in the dictionary dict, otherwise returns FALSEDIT.ITEMS () # Returns the iterated (key, value) tuple array Dit.keys () # in the list Returns a dictionary of all keys Dit.setdefault (' Subject ', ' Python ') # and get () similar, but if the key does not already exist in the dictionary, the key will be added and the value will be set to Defaultdit.update (DICT2) # Update the key/value pairs of the dictionary dict2 to dict DIT.VAlues () # Returns all values in the dictionary as a list dit.clear () # Delete all elements in the dictionary 

Eight, Ganso

A python tuple (tuple) is similar to a list, except that the elements of a tuple cannot be modified; tuples use parentheses (), and the list uses square brackets []; tuple creation is simple, just add elements in parentheses and separate them with commas (,).

#-*-Coding:utf-8-*-tup1 = (' Physics ', ' Chemistry ', 1997, $) tup2 = (1, 2, 3, 4, 5) Tup3 = "A", "B", "C", "D" # Access tuple Prin T "Tup1[0]:", Tup1[0]  # physicsprint "Tup1[1:3]:", Tup1[1:3]  # (' Chemistry ', 1997) # Modify Tuple Tup4 = Tup1 + tup2print Tup4  # (34.56, ' abc ', ' XYZ ') # Delete tuple Tup = (' Tup3 ', ' Tup ', 1997, $) Print Tupdel tup# tuple index & intercept L = (' spam ', ' Spam ', ' spam! ') Print L[0] #  Spamprint l[1]  # spamprint l[2]  # ' spam! ' Print l[-2]  # ' Spam ' Print l[1:]  # [' Spam ', ' spam! '] # tuple built-in function print CMP (TUP3, tup2)  # compares two tuple elements. Len (TUP3)  # Calculates the number of tuple elements. Max (TUP3)  # Returns the element's maximum value in a tuple. Min (tup3)  # Returns the element minimum value in the tuple. L = [1, 2, 3, 4]print lprint tuple (L)  # Converts the list to tuples.

Nine, define the string

\ n indicates a newline \ t means a tab \ \ means \ character itself

Ten, Unicode string

Python default encoding ASCII encoding #-*-Coding:utf-8-*-

Xi. Conversion of numeric types

int (x [, Base]) converts x to an integer, float (x) converts x to a floating-point number complex (real [, Imag]) creates a complex number str (x) to convert the object x to a string repr (x) to convert the object x to the expression string eval (St R) is used to calculate a valid Python expression in a string and returns an object tuple (s) converts the sequence s to a tuple list (s) converts the sequence s to a list Chr (x) converts an integer to a character unichr (x) Converts an integer to a Unicode character ord (x) converts a character to its integer value hex (x) converts an integer to a hexadecimal string Oct (x) converts an integer to an octal string