What is a list compression in Python?
Hello Everyone, I am not sure if I have posted this question in a correct board. Can anyone please teach me: What is a list compression in Python? Would you mind give me some list compression examples? Thanks & really appreciate that. Kit -- http://mail.python.org/mailman/listinfo/python-list
Re: What is a list compression in Python?
Thank you so much guys. Just out of curiosity: can I do something like this to "square all even numbers in the range 1-10"? print [x^2 for x in range (1,11) if x % 2 == 0] Or is there a better way of doing it? Thanks for the help, and I am really appreciate your help. Kit. On 1月19日, 上午12時30分, Steven D'Aprano wrote: > On Mon, 18 Jan 2010 08:07:41 -0800, Kit wrote: > > Hello Everyone, I am not sure if I have posted this question in a > > correct board. Can anyone please teach me: > > > What is a list compression in Python? > > Google "python list comprehension". > > If Google is broken for you, try Yahoo, or any other search engine. > > > Would you mind give me some list compression examples? > > Instead of this: > > L = [] > for x in range(10): > L.append(x**2) > > you can write: > > L = [x**2 for x in range(10)] > > Instead of this example: > > L = [] > for x in range(10): > if x % 2 == 0: > L.append(x**2) > > you can write: > > L = [x**2 for x in range(10) if x % 2 == 0] > > -- > Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: What is a list compression in Python?
Oops... > print [x^2 for x in range (1,11) if x % 2 == 0] print [x^2 for x in range (1,10) if x % 2 == 0] On 1月19日, 上午8時24分, Kit wrote: > Thank you so much guys. > > Just out of curiosity: can I do something like this to "square all > even numbers in the range 1-10"? > print [x^2 for x in range (1,11) if x % 2 == 0] > > Or is there a better way of doing it? Thanks for the help, and I am > really appreciate your help. > > Kit. > > On 1月19日, 上午12時30分, Steven D'Aprano > > > cybersource.com.au> wrote: > > On Mon, 18 Jan 2010 08:07:41 -0800, Kit wrote: > > > Hello Everyone, I am not sure if I have posted this question in a > > > correct board. Can anyone please teach me: > > > > What is a list compression in Python? > > > Google "python list comprehension". > > > If Google is broken for you, try Yahoo, or any other search engine. > > > > Would you mind give me some list compression examples? > > > Instead of this: > > > L = [] > > for x in range(10): > > L.append(x**2) > > > you can write: > > > L = [x**2 for x in range(10)] > > > Instead of this example: > > > L = [] > > for x in range(10): > > if x % 2 == 0: > > L.append(x**2) > > > you can write: > > > L = [x**2 for x in range(10) if x % 2 == 0] > > > -- > > Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: What is a list compression in Python?
Cool! Thank you very much. You mean this instead right? print [x*x for x in xrange(1,11,2)] Kit On 1月19日, 上午8時36分, Gary Herron wrote: > Kit wrote: > > Thank you so much guys. > > > Just out of curiosity: can I do something like this to "square all > > even numbers in the range 1-10"? > > print [x^2 for x in range (1,11) if x % 2 == 0] > > > Or is there a better way of doing it? Thanks for the help, and I am > > really appreciate your help. > > That's a fine way to do it, although: > > xrange is slightly more efficient than range for large > sets of values. (This isn't such a large set for it to matter.) > > You can get range and xrange to count by two's, eliminating > the need for the "if" portion in this case. > > The exponent operator is ** not ^, and x*x is more efficient than x**2. > > So. > > print [x**2 for x in xrange(1,11,2)] > > Gary Herron > > > > > Kit. > > > On 1月19日, 上午12時30分, Steven D'Aprano > cybersource.com.au> wrote: > > >> On Mon, 18 Jan 2010 08:07:41 -0800, Kit wrote: > > >>> Hello Everyone, I am not sure if I have posted this question in a > >>> correct board. Can anyone please teach me: > > >>> What is a list compression in Python? > > >> Google "python list comprehension". > > >> If Google is broken for you, try Yahoo, or any other search engine. > > >>> Would you mind give me some list compression examples? > > >> Instead of this: > > >> L = [] > >> for x in range(10): > >> L.append(x**2) > > >> you can write: > > >> L = [x**2 for x in range(10)] > > >> Instead of this example: > > >> L = [] > >> for x in range(10): > >> if x % 2 == 0: > >> L.append(x**2) > > >> you can write: > > >> L = [x**2 for x in range(10) if x % 2 == 0] > > >> -- > >> Steven -- http://mail.python.org/mailman/listinfo/python-list
