@spr, thanks for the explanation, especially on representations of strings. To think that i freely used repr(variable_x) without fully understanding the meaning and the power of that function..
On Mon, Feb 22, 2010 at 9:37 AM, spir <denis.s...@free.fr> wrote: > Just a little complement to Steven's excellent explanation: > > On Mon, 22 Feb 2010 10:01:06 +1100 > Steven D'Aprano <st...@pearwood.info> wrote: > > [...] > > > So if you write a pathname like this: > > > > >>> path = 'C:\datafile.txt' > > >>> print path > > C:\datafile.txt > > >>> len(path) > > 15 > > > > It *seems* to work, because \d is left as backlash-d. But then you do > > this, and wonder why you can't open the file: > > I consider this misleading, since it can only confuse newcomers. Maybe > "lonely" single backslashes (not forming a "code" with following > character(s)) should be invalid. Meaning literal backslashes would always be > doubled (in plain, non-raw, strings). What do you think? > > > But if the escape is not a special character: > > > > >>> s = 'abc\dz' # nothing special > > >>> print s > > abc\dz > > >>> print repr(s) > > 'abc\\dz' > > >>> len(s) > > 6 > > > > The double backslash is part of the *display* of the string, like the > > quotation marks, and not part of the string itself. The string itself > > only has a single backslash and no quote marks. > > This "display" is commonly called "representation", thus the name of the > function repr(). It is a string representation *for the programmer* only, > both on input and output: > * to allow one writing, in code itself, string literal constants containing > special characters, in a practical manner (eg file pathes/names) > * to allow one checking the actual content of string values, at testing > time > > The so-called interactive interpreter outputs representations by default. > An extreme case: > >>> s = "\\" > >>> s > '\\' > >>> print s, len(s) > \ 1 > >>> print repr(s), len(repr(s)) > '\\' 4 > >>> > The string holds 1 char; its representation (also a string, indeed) holds > 4. > > > The best advice is to remember that Windows allows both forward and > > backwards slashes as the path separator, and just write all your paths > > using the forward slash: > > > > 'C:/directory/' > > 'C:textfile.txt' > > Another solution is to take the habit to always escape '\' by doubling it. > > > Denis > ________________________________ > > la vita e estrany > > http://spir.wikidot.com/ > _______________________________________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor > -- Regards, Sithembewena Lloyd Dube http://www.lloyddube.com
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