python - What is the difference between a[:]=b and a=b[:] -

- 

a=[1,2,3] b=[4,5,6] c=[] d=[]

whats difference between these 2 statements?

c[:]=a d=b[:]

but both gives same result.

c [1,2,3] , d [4,5,6]

and there difference functionality wise?

c[:] = a means replace elements of c elements of a

>>> l = [1,2,3,4,5] >>> l[::2] = [0, 0, 0] #you can replace particular elements using  >>> l [0, 2, 0, 4, 0]  >>> k = [1,2,3,4,5] >>> g = ['a','b','c','d'] >>> g[:2] = k[:2] # replace first 2 elements >>> g [1, 2, 'c', 'd']  >>> = [[1,2,3],[4,5,6],[7,8,9]] >>> c[:] =      #creates shallow copy >>> a[0].append('foo') #changing mutable object inside changes in c >>> [[1, 2, 3, 'foo'], [4, 5, 6], [7, 8, 9]] >>> c [[1, 2, 3, 'foo'], [4, 5, 6], [7, 8, 9]]

d = b[:] means create shallow copy of b , assign d , similar d = list(b)

>>> l = [1,2,3,4,5] >>> m = [1,2,3] >>> l = m[::-1]  >>> l [3,2,1]  >>> l = [[1, 2, 3], [4, 5, 6], [7, 8, 9]] >>> m = l[:] #creates shallow copy  >>> l[0].pop(1) # mutable object inside l changed, affects both l , m 2 >>> l [[1, 3], [4, 5, 6], [7, 8, 9]] >>> m [[1, 3], [4, 5, 6], [7, 8, 9]]

Comments

Post a Comment

Popular posts from this blog

c# - SVN Error : "svnadmin: E205000: Too many arguments" -

-
i trying reposotries using c# code process svncommand = null; var psi = new processstartinfo("svnadmin"); psi.redirectstandardoutput = true; psi.redirectstandarderror = true; psi.useshellexecute = false; psi.arguments= @"dump c:\repositories\myrepo > c:\temp\myrepodumpfile.dump"; using (svncommand = process.start(psi)) { var myoutput = svncommand.standardoutput; var myerror = svncommand.standarderror; debug.write("output :" + environment.newline + environment.newline + myoutput.readtoend() + environment.newline + "error :" + environment.newline + environment.newline + myerror.readtoend()); svncommand.close(); } when use dump command commandline svnadmin dump c:\repositories\myrepo > c:\temp\myrepodumpfile.dump it works fine when try ...
Read more

c# - Copy ObservableCollection to another ObservableCollection -

-
how copy observablecollection item observablecollection without reference of first collection? here observablecollection item value changes affecting both collections. code private observablecollection<ratemodel> _allmetalrate = new observablecollection<ratemodel>(); private observablecollection<ratemodel> _metalrateondate = new observablecollection<ratemodel>(); public observablecollection<ratemodel> allmetalrate { { return this._allmetalrate; } set { this._allmetalrate = value; notifypropertychanged("metalrate"); } } public observablecollection<ratemodel> metalrateondate { { return this._metalrateondate; } set { this._metalrateondate = value; notifypropertychanged("metalrateondate"); } } foreach (var item in metalrateondate) allmetalrate.add(item); what causing , how can solve it? you need clone object referenced item before it's a...
Read more

All overlapping substrings matching a java regex -

-
is there api method returns (possibly overlapping) substrings match regular expression? for example, have text string: string t = 04/31 412-555-1235; , , have pattern: pattern p = new pattern("\\d\\d+"); matches strings of 2 or more characters. the matches are: 04, 31, 412, 555, 1235. how overlapping matches? i want code return: 04, 31, 41, 412, 12, 55, 555, 55, 12, 123, 1235, 23, 235, 35. theoretically should possible -- there obvious o(n^2) algorithm enumerates , checks substrings against pattern. edit rather enumerating substrings, safer use region(int start, int end) method in matcher . checking pattern against separate, extracted substring might change result of match (e.g. if there non-capturing group or word boundary check @ start/end of pattern). edit 2 actually, it's unclear whether region() expect zero-width matches. specification vague, , experiments yield disappointing results. for example: string line = "xx90xx"; strin...
Read more