python27读书笔记0.3

#-*- coding:utf-8 -*-

##D.has_key(k): A predicate that returns True if D has a key k.
##D.items(): Returns the contents of dictionary D as a list of two-element tuples(k,v),
##D.iteritems():Returns an iterator that generates the values from dictionary D as
##a sequence of two-element tuples(k,v).

##signals = {0:'red',1:'yellow',2:'green'}
##print signals.items()
##
##for i in signals.items():
## print i
##
##for i,k in signals.items():
## print i ,k
##
##
##signalScan = signals.iteritems()
##
##print signalScan
##
##for n,name in signalScan:
## print "{0:04d}:{1}".format(n,name)
## print '--------------------'
## print n,name

##D.iterkeys():Return an iterator that generates the keys from dictionary D.
##D.itervalues():Returns an iterator that generates the values from dictionary D.
##D.keys():Returns a list of the key values in dictionary D,in no particular order.
##D.popitem():Returns an arbitrary entry from dictionary D as a(key,value) tuple,
##and also removes that entry.If D id empty,raises a KeyError exception.
##D.setdefault(k,x):If dictionary D has a key equal to k,this method returns the
##corresponding value D[k].If D has no key equal to k,the method returns the default
##value X.However,unlike the .get() method,it also creates a new key-value pari(k,x) in D.
##As with the .get() method,the second argument is optional,and defaults to the value None.
##D.values():Returns a list of the values from key-value pairs in dictionary D,in no particular order.
##Howerver,if you call both the .items() and .values() methods of a dictionary
##without changing that dictionary's contnts between those calls,Python guarantees that
##the ordering of the two results will be the same .

##signals = {0:'red',1:'yellow',2:'green'}
##print signals.values()
##print signals.keys()

##D.update(D2)
##Merge the contents of dictionary D2 into dictionary D.For any key-value pairs that have the
##same key in both D and D2,the value for that key in D after this operation will be the
##value from D2,not the value form D.

##roster={1:'zen',2:'peter',3:'jone',4:'joy'}
##newer={3:'bev',5:'GoodN'}
##
##print '---roster:'
##print roster
##print '---after update:'
##roster.update(newer)
##print roster
##print '--new:'
##print newer

##--- Dictionary comprehensions ---
##As with list comperhensions,you provide one or more for clauses and an optional if clause.
##For all possible combinations of the values in the for clauses that have a true value
##for the if clause,two expressions ek and ev are evaluated,and a new dictionary entry is
##added with key ek and value ev.

## --- Type file:Input and output files ---
##To open a file,use this general form:
##f = open(name[,mode[,bufsize]]])
##name
## The path name of the file to be opened,as string.
##mode
## An optional string specifying what ypu plan to do with the file.
##If omitted,you will get read access to the file.In general the value consists of three parts:
## General mode,one of :
## r:Read access.The file must alread exist.You will not be allowed to write to it.
## w:Write access.If there is no file by this name,a new one will be created.
## If there is an existing file,it will be deleted!
## a:Append access.If there is a file by this name,your initial position will be at the end of
## the file,and you will be allowed to write(and read).If there is no file by this name,
## a new one will be created .On some systems,all writes to a file with append mode are
## added at end of the file,regardless of the current file position.
## If you plan to modify the file,append a "+" next.
## For example,mode "r+" puts you at the beginning of an existing file and
## allows you to write to the file anywhere.
## Mode "w+" is the same as "w":it deletes an existing file if there is any,
## then creates a new file and givers you write access.
## Mode "a+" allows you to write new data at the end of an existing file;if no
## file by this name exists,it will crate a new one.
## If you handing binary data ,as opposed to lines of text,add "b" at the end of the mod string.
## For modes beginning with 'r',you may append a capital 'u' to request universal newline
## treatment.This is handy when you are reading files made on a platform with different line
## termination conventions.
## When reading lines from a file opened in this way,any line terminator('\n','\r',or'\r\n')
## will appear in the return value as the standard '\n'.Also,files so opened will have an attribute
## named .newlines;this attribute will be None initially,but after any line terminators
## have been read,it will be a tuple containing all the different line terminator strings seen so far.
##
##bufsize
## Buffer size:this affects when phsical device writes are done,compared to write operations that
## your program performs.
## In most cases you will probably want to omit this argument.The default is to use
## line buffering for terminal-type devices,or some system default for other devices.
## Use 0 to force unbuffered operation.This may be inefficient,but any file writes are performed immediately.
## Use 1 for line buffering:output lines are written whenever you write a line terminator such as '\n'.
## Use larger values to specify the actual size of the buffer.
## Use a negative value to request the system defaults.
##If you are reading text files,and you do not want to worry about the variety of line termination
##protocole,you may use a mode value of "U" for "universal line terminator mode."
##In this mode,input lines may be terminated with either carriage return('\r'),newline('\n'),or both,
##but the lines you receive will always be terminated with a single newline.
##A file is its own iterator.Hence,if you have a file inFile opened for reading,you can use
##a for loop that looks like this to iterate over the lines of the file:
## for line in inFile:
## ....
##The variable line will be set to each line of the file in turn.The line terminator character(if any) will be present
##in that string .
##Other aspects of files:
##
##Every open file has a current position.Initially ,this will 0L if you opened it for reading or writing,
##or the size of the file if you opened it with append access.Each write or read operation
##moves this position by the amount read or written.You can also query or set the file position;
##Files may use a technique called buffering.Because phusical access to some storage
##media(such a disk drivers) takes a relatively long time,Python may employ a storage area called a buffer as a
##holding area for data being input or output.
##For example,if you are writing data to a disk file,Python may keep the data in the file's buffer area
##until the buffer is full and only then actually write it to the physical disk.There are various techniques
##for controlling this behavior;

##--- Methods on file objects ---
##Use these methods on an open file instance F.
##F.close()
## Close file F. Any unwritten data in the buffer will be flushed. No further operations
## will be allowed on thefile unless it is reopened with the open() function.
##F.flush()
## For buffered files,you can use this method to make sure that all data written to the file has
## been physically transmitted to the storage medium.Closing a file will also flush the buffer.
## Avoid using this method unless you really need it,as it may make your program less efficient.
##F.isatty()
## A predicate that tests whether F is a terminal;"tty" is an ancient term that originally meant
## "Teletype",but has come to mean any terminal or simulated terminal.
##F.read(n)
## Read the next n characters from F and return them as a string.
## If there are fewer than n characters remaining after your current position,you will get all remaining
## characters.If you are at the end of the file,you will get back an empty string ('').
## The argument is optional.If omitted,you will get the entire remaining contents of the file as a string.
##F.readline(maxlen)
## Read the next textline from F and return it as a string,including the line terminator if any.
## If you need to limit the maximum size of incoming lines,pass that size limit as the optional maxlen
## argument.The default is to return a line of any size (subject to memory limitations).If the line
## exceeds maxlen,the file position will be left pointing to the first unread character of that line.
##F.readlines()
## Read all remaining lines from F and return them as a list of strings,including line terminator characters if any.
##F.seek(offset,whence)
## Change the file's current position.The value of whence determines how the offset value is used
## to change the posititon:
## 0:Set the position to offset byetes after the beginning of the file.
## 1:Move the current position offset bytes toward the end of the file.
## 2:Move the current position offset bytes relative to the end of the file.
## For example,for a file f, this operation would set the position to 4 bytes before the end of the file:
## f.seek(-4,2)
##F.tell()
## This method returns the current file position relative to the beginning as a long value.
##F.write(s)
## Write the contents of string s to file F. This operation will not add terminator characters;
## if you want newlines in your file,include them in the string s.
##F.writelines(s)
## For a sequence s containing strings,write all those strings to F.No line terminators will be add;
## you must provide them explicitly if you want them.

## --- None:The special placeholder value ---
##Python has a unique value called None. This special null value can be used as a placeholder,
##or to signify that some value is unknow.
##In conversational mode,any expression that evaluates to None is not printed.However,if a value
##of None is converted to a string,the result is the string 'None';this may happen ,for example,
##in a print statement.
##The value None is returned from any function that executes a return statement with no value,or
##any function after it exectes its last line if that last line is not a return statement.

## --- Operators and expressions ---
##Python's operations are shown here from highest precedence to lowest,with a ruled line separation
##groups of operators with equal precedence:
## (E) Parenhesize expression or tuple.
## [E,...] List.
## {key:value,...} Dictionary
## '...' Convert to string representation
## x.attribute Attribute reference.
## x[...] Subscript or slice;
## f(...) Call function f.
## x**y x to the y power.
## -x Negation.
## ~x Bitwise not(one's complement).
## x*y Multiplication
## x/y,x//y Division.The"//" form discards the fraction from the result."13.9//5.0"returns the value 2.0
## x%y Modulo (remainder of x/y).
## x+y Addition,concatenation.
## x-y Subtraction.
## x<<y x shifted left y bits.
## x>>y x shifted right y bits
## x&y Bitwise and.
## x^y Bitwise exclusive or.
## x|y Bitwise or.
## x<y,x<=y,x>y,x>=y,x!=y,x==y Comparisons.These operators are all predicates;
## x in y,x not in y Test for membership.
## x is y,x in not y Test for identity.
## not x Boolen "not"
## x and y Boolen "and"
## x or y Boolen "or"

##What is an iterable?
##To iterate over a sequence means to visit each element of the sequence,and do some
##operation for each element.
##In Python,we say that a value is an iterable when your program can iterate over it.
##In short,an iterable is a value that represents a sequence of one more values.
##All instances of Python's sequence types are iterables.
##These types may be referred to as container types: a unicode string is a container for
##32-bit characters,and lists and tuples are general-purpose cantainers that can contail
##any sequence.

## --- Basic functions ---
##abs():Absolute value.To find the absolute value of a number x.
##all():Are all the elements of an iterable true?
##any():Are any of the members of an iterable true?
##bin():convert to binary.
##This function takes an integer artument and returns a string that represents that
##number in binary
##bool():Conbert to Boolean
##This function tabkes any value x and converts it to a Boolean(True or False) value.
##bytearray():Create a byte array
##chr():Get the character with a given code
##For arguments n in the reage 0 to 255,this function returns a one-character string
##containing the character that has code n.
##ord():Find the numeric code for a character
##cmp():Compare two values
##cmp(x,y)
##The return value is :
## a negative number if x if less than y
## Zero if x is equal to y.
## A positive number if x is greater than y.
##
##complex():Convert to complex type
##To create a complex number from a real part R and a complex part I:
##dict():convert to a dictionary
##This function creates a new dictionary from its arguments.
##divmod():Quotient and remainder
## Examples: divmod(13,5) return (2,3)
##enumerate():Step through indices and values of an iterable

##L = ['Ministry', 'of', 'Silly', 'Walks']
##for where, what in enumerate(L):
## print "[{0}] {1}".format(where,what)
##
##print "---begin with 1 ---"
##for where, what in enumerate(L,1):
## print "[{0}] {1}".format(where,what)
##print "---begin with 3 ---"
##for where, what in enumerate(L,3):
## print "[{0}] {1}".format(where,what)

##filter():Extract qualifying elements from an iterable
##This function is useful for removing some of the elements of an iterable.
##You must provide a filtering function that takes one arguments and returns
##a bool value.

##def isOdd(x):
## if (x%2) == 1: return True
## else: return False
##Li=filter(isOdd, [88, 43, 65, -11, 202])
##print Li
##
##def isLetter(c):
## return c.isalpha()
##print filter(isLetter, "01234abcdeFGHIJ*(&!^")

##maybes = [0, 1, (), (2,), 0.0, 0.25]
##print filter(None, maybes)
##print '---arguments with bool---'
##print filter(bool, maybes)

##float():Convert to float type
##format():Format a value
##frozenset():Create a frozen set (an immutable set)
##hex():Convert to base 16
##Given an integer,this function returns a string display that value in hexadecimal.

##print hex(15)
##print hex(255)
##
##int():Convert to int type
##input():Read an expression from the user
##iter():Produce an iterator over a sequence
##len():Number of elements
##list():Convert to a list
##long():convert to long type
##map():Apply a function to each element of an iterable
##map(f,s):f is a function that takes one argument and returns a value.
## s is any iterable.

##def add100(x):
## return x+100
##Li = map(add100, (44,22,66))
##print Li
##
##def abc(a, b, c):
## return a*10000 + b*100 + c
##L2 = map(abc, (1,2,3), (4, 5, 6), (7, 8, 9))
##print '---- L2 -- '
##print L2
##
##print map(None, range(3), 'abc', [44, 55, 66])

##max(): Largest element of an iterable
##min(): Smallest element of an iterable
##next(): Call an iterator

##it = iter(xrange(0,2))
##print next(it, 'Done')
##print next(it, 'Done')
##print next(it, 'Done')
##print next(it, 'Done')

##oct():Convert to base 8
##open():Open a file
##ord():Find the numberic code for a character
##pow():Exponentiation

##print pow(2,4)
##print 2**9
##print (2**9)%3
##print pow(2,9,3)

##range():Generate an arithmetic progression as a list
##raw_input():Prompt and read a string from the user

reduce():Sequence reduction
reversed():Produce a reverse iterator
round():Round to the nearest integral value
set():Create an algebraic set
sorted():Sort a sequence
str():Convert to str type
sum():Total the elements of a sequence
tuple():convert to a tuple.
type():Return a value's type.
unichr():Convert a numeric code to a Unicode character.
unicode():conbert to a Unicode string
xrange():Arithmetic progression generator
The xrange() function has exactly the same arguments as the range() function.
The didfference is that xrange() is a generator,while rang() actually builds a
list for its result.This means you can use xrange() in situations where you
want to generate a large series of the values from an arithmetic progression,
but you do not have engough memory to build that serise as a list.
zip():Combine multiple sequences
The purpose of this function is to build a list of tuples from two or more iterables
of the same length.