Python Fundamental for Django

Strings

>>> s = ' Django is cool ' >>> words = S.split () >>> words[' Django ', ' is ', ' cool ']>>> '. Join (words) ' Django is cool ' >>> s.count (' o ') 3>>> s.find (' Go ') 4>>> s.replace (' Django ', ' Python ') ' Python is cool '

Some of the commonly used string functions:

String method	Description
count	number of occurrences of Substring in string
find	Search for substring [also see index, RFind, Rindex]
Join	Merge substrings to single delimited string
replace	S Earch and replace (sub) string
split	split delimited string to substrings [also see SP Litlines]
startswith	Does string start with substring [also see endswith]
Strip	Remove leading and trailing whitespace [also see Rstrip, Lstrip]
title	title-case string [Also see capitalize, Swapcase]
Upper	uppercase string [also see lower]
isupper	is the string all uppercase? [Also see islower, and so forth]

Formatted output:

>>> '%s is number%d ' percent (' python ', 1) ' Python is number 1 ' >>> hi = ' hellobaby ' >>> hi ' hello\n Baby ' >>> print Hihellobaby

Tuples

The elements inside a tuple cannot be modified, which is related to its own implementation mechanism, and it is a good choice to pass parameters if you do not want them to be modified.

>>> a = (' One ', ' one ') >>> a[0] ' one ' >>> c = (' Only ',) >>> c[0] "only" >>> d = ' on Ly ',>>> d[0] ' only '

It is important to note that when declaring a tuple, the key is a comma, and if not the following example is just a string, note that this is significant because many Django data types use a tuple:

>>> B = (' Only ') >>> b[0] ' o '

Dictionaries

A dictionary is a list of a sort of hash table with elements that have key and value two attributes. The elements of a dictionary can be modified, unordered, and size can vary. Such as:

>>> book = {' title ': ' Django ', ' Year ':2008}>>> ' title ' in Booktrue>>> book.get (' Pub ', ' N/a ') ' N/A ' >>> book[' pub '] = ' addision ' >>> book.get (' Pub ', ' N/A ') ' Addision ' >>> for key in book:...< C0/>print key, ': ', book[key]...year:2008title:djangopub:addision

Some common functions:

Dictionary Method	Description
Keys	Keys (also see Iterkeys)
Values	Values (also see itervalues)
Items	Key-value pairs (also see ITERITEMS)
Get	Get value given key else default [also see SetDefault, Fromkeys]
Pop	Remove key from Dict and return value [also see clear, Popitem]
Update	Update Dict with contents of (a) other dict

Enumerate

>>> data = Enumerate ((123, ' abc ', ' Hello ') >>> for I, value in data: ...     Print I, Value ... 0 1231 ABC2 Hello

Exception Handling

If you try to open a file with exception handling:

Try:    f = open (filename, ' r ') except IOError, E:    return False, str (e)

You can also put a variety of error types into a tuple, one-off detection:

Try:    Process_some_data () except (TypeError, ValueError,...), E:    print "ERROR", E

Of course, different types of exceptions can be handled differently, and in the last case a exception is usually added, as this can include all the exception conditions:

Try: ...    except (TypeError, ValueError), E:    ... except Arithmeticerror, E:    ... except Exception, E:    ...

Files

>>> f = open (' Test.txt ', ' W ') >>> f.write (' foo\n ') >>> f.write (' bar\n ') >>> f.close ( ) >>> f = open (' Test.txt ', ' R ') >>> for line in F: ...     Print Line.rstrip () ...foobar>>> f.close ()

Anonymous Functions

The anonymous function uses the keyword, which consists of lambda an expression that represents the return value of the function. The usual way to use:

Lambda args:expression

Sorted (list_of_people, key = Lambda person:person.last_name) # equivalent to Def get_last_name (person):    return Person.last_ Namesorted (list_of_people, key = Get_last_name)

* Args and * * Kwargs

Python inside the * is not a C language inside the pointer, as a parameter when passed, * represents a tuple (list), * * Represents dict

Examples are as follows:

def check_web_server (host, port, path):    ...

General usage when calling a function:

Check_web_server (' 127.0.0.1 ', 8080, '/admin/')

If the parameter is used as a tuple or dict, the parameter can be passed in the form of a subscript, but it is very convenient to complete the parameters in the way of *:

Host_info = (' www.python.org ', +, '/') Check_web_server (host_info[0],host_info[1], host_info[2]) check_web_server (* Host_info) Host_info = {' host ': ' www.python.org ', ' Port ': ', ' path ': '/'}check_web_server (**host_info)

Dynamic instantiation

Unlike some of the other programming languages, Python supports dynamic instantiation of classes, such as:

>>> class Book (object): ...     def __init__ (self, name): ...         Self.name = name...>>> John = Book (' John ') >>> john.father = ' Jack ' >>> print John.fatherjack

Python Fundamental for Django