Usually I struggle a short while with \ and either succeed or give up. Today I'm in a different mood and don't give up. So here is my question:
You have an unknown character string c such as '\n' , '\a' , '\7' etc.
How do you echo them using print?
print_str( c ) prints representation '\a' to stdout for c = '\a' print_str( c ) prints representation '\n' for c = '\n' ...
It is required that not a beep or a linebreak shall be printed.
First of all it has be remarked that it is impossible to a certain extent. That's because e.g. c = '\a' and c = '\7' do represent the same string but this ambiguity doesn't occur for many numbers. But lets weaken the requirement and fix a canonical representation in case of ambiguity. I'm still getting stuck here.
Kay Schluehr wrote: > Usually I struggle a short while with \ and either succeed or give up. > Today I'm in a different mood and don't give up. So here is my > question:
> You have an unknown character string c such as '\n' , '\a' , '\7' etc.
> How do you echo them using print?
> print_str( c ) prints representation '\a' to stdout for c = '\a' > print_str( c ) prints representation '\n' for c = '\n' > ...
> It is required that not a beep or a linebreak shall be printed.
> First of all it has be remarked that it is impossible to a certain > extent. That's because e.g. c = '\a' and c = '\7' do represent the same > string but this ambiguity doesn't occur for many numbers. But lets > weaken the requirement and fix a canonical representation in case of > ambiguity. I'm still getting stuck here.
I don't understand the question. Wouldn't the canonical representation be repr(c) or repr(c)[1:-1]?
Sybren Stuvel wrote: > Kay Schluehr enlightened us with: > > Usually I struggle a short while with \ and either succeed or give up. > > Today I'm in a different mood and don't give up. So here is my > > question:
> > You have an unknown character string c such as '\n' , '\a' , '\7' etc.
> > How do you echo them using print?
> > print_str( c ) prints representation '\a' to stdout for c = '\a' > > print_str( c ) prints representation '\n' for c = '\n' > > ...
> > It is required that not a beep or a linebreak shall be printed.
> try "print repr(c)".
This yields the hexadecimal representation of the ASCII character and does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the escape semantics. One way to achieve this naturally is by prefixing '\a' with r where r'\a' indicates a "raw" string. But unfortunately "rawrification" applies only to string literals and not to string objects ( such as c ). I consider creating a table consisting of pairs {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe I've overlooked some simple function or trick that does the same for me.
> This yields the hexadecimal representation of the ASCII character and > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > escape semantics.
But you yourself noted earlier that '\a' and '\x07' are the same string and said:
> But lets weaken the requirement and fix a canonical representation in > case of ambiguity.
That's exactly what repr(c) does, it uses a canonical representation with '\t', '\r', '\n', '\\', (and when it has to "\'", '\"') using the short escape form (because they are so commonly used), and the all the other (more obscure) escape sequences using the hexadecimal form.
BTW, c.encode('string_escape') is another way to convert a string to almost the same escaped form (except for a minor difference in the treatment of quote characters).
> But unfortunately "rawrification" applies only to string literals and > not to string objects ( such as c ).
Oh dear, the fact that you could even consider writing that sentence seems to show a fundamental misunderstanding of what a raw string literal means.
>>>Usually I struggle a short while with \ and either succeed or give up. >>>Today I'm in a different mood and don't give up. So here is my >>>question:
>>>You have an unknown character string c such as '\n' , '\a' , '\7' etc.
>>>How do you echo them using print?
>>>print_str( c ) prints representation '\a' to stdout for c = '\a' >>>print_str( c ) prints representation '\n' for c = '\n' >>>...
>>>It is required that not a beep or a linebreak shall be printed.
>>try "print repr(c)".
> This yields the hexadecimal representation of the ASCII character and > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > escape semantics. One way to achieve this naturally is by prefixing > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > "rawrification" applies only to string literals and not to string > objects ( such as c ). I consider creating a table consisting of pairs > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > I've overlooked some simple function or trick that does the same for > me.
No, you've overlooked the fact that if you print the string containing the two characters "backslash" and "lower case a" then it will print exactly those two characters. See:
Steve Holden wrote: > Kay Schluehr wrote: > > Sybren Stuvel wrote:
> >>Kay Schluehr enlightened us with:
> >>>Usually I struggle a short while with \ and either succeed or give up. > >>>Today I'm in a different mood and don't give up. So here is my > >>>question:
> >>>You have an unknown character string c such as '\n' , '\a' , '\7' etc.
> >>>How do you echo them using print?
> >>>print_str( c ) prints representation '\a' to stdout for c = '\a' > >>>print_str( c ) prints representation '\n' for c = '\n' > >>>...
> >>>It is required that not a beep or a linebreak shall be printed.
> >>try "print repr(c)".
> > This yields the hexadecimal representation of the ASCII character and > > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > > escape semantics. One way to achieve this naturally is by prefixing > > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > > "rawrification" applies only to string literals and not to string > > objects ( such as c ). I consider creating a table consisting of pairs > > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > > I've overlooked some simple function or trick that does the same for > > me.
> No, you've overlooked the fact that if you print the string containing > the two characters "backslash" and "lower case a" then it will print > exactly those two characters. See:
> In [30]: c = "\\a"
> In [31]: len(c) > Out[31]: 2
> In [32]: print c > \a
I'm interested in the transition between two literals from which one is a string literal containing \ as a "meta character" s.t. '\a' has actually length 1 and is beep when printed to stdout and its "raw" form without a meta character interpretation of \ that leads to the result you described. Using the string prefix r to '\a' indicates the raw form to the compiler. But there seems to be no runtime counterpart. I've suggested a naive implementation such as
def rawform(c): return {'\a': r'\a'}[c]
Here the function returns for the single input character '\a' the two character raw form by means of escaping \ ( and raises a KeyError exception otherwise ).
>>> c = '\a' >>> print rawform(c)
\a
This has the same effect as writing:
>>> c = r'\a' >>> print c
\a
But there is some ambiguity due to the the fact that applying '\7' to rawform() yields r'\a' and not r'\7'. So one needs more specification for disambiguation using e.g. an extra parameter.
> But there is some ambiguity due to the the fact that applying '\7' to > rawform() yields r'\a' and not r'\7'. So one needs more specification > for disambiguation using e.g. an extra parameter.
>>> '\a'=='\7' True
The two are actually the same thing, so how could a function decide whether to return '\\a' or '\\7'.
It's like asking the following: >>> c = 04 >>> print rawform(c) 04
>>> c = 4 >>> print rawform(c) 4
which is obviously not possible, neither of any use imho.
>>>>>Usually I struggle a short while with \ and either succeed or give up. >>>>>Today I'm in a different mood and don't give up. So here is my >>>>>question:
>>>>>You have an unknown character string c such as '\n' , '\a' , '\7' etc.
>>>>>How do you echo them using print?
>>>>>print_str( c ) prints representation '\a' to stdout for c = '\a' >>>>>print_str( c ) prints representation '\n' for c = '\n' >>>>>...
>>>>>It is required that not a beep or a linebreak shall be printed.
>>>>try "print repr(c)".
>>>This yields the hexadecimal representation of the ASCII character and >>>does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the >>>escape semantics. One way to achieve this naturally is by prefixing >>>'\a' with r where r'\a' indicates a "raw" string. But unfortunately >>>"rawrification" applies only to string literals and not to string >>>objects ( such as c ). I consider creating a table consisting of pairs >>>{'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe >>>I've overlooked some simple function or trick that does the same for >>>me.
>>No, you've overlooked the fact that if you print the string containing >>the two characters "backslash" and "lower case a" then it will print >>exactly those two characters. See:
>>In [30]: c = "\\a"
>>In [31]: len(c) >>Out[31]: 2
>>In [32]: print c >>\a
> I'm interested in the transition between two literals from which one is > a string literal containing \ as a "meta character" s.t. '\a' has > actually length 1 and is beep when printed to stdout and its "raw" form > without a meta character interpretation of \ that leads to the result > you described. Using the string prefix r to '\a' indicates the raw form > to the compiler. But there seems to be no runtime counterpart. I've > suggested a naive implementation such as
> def rawform(c): > return {'\a': r'\a'}[c]
> Here the function returns for the single input character '\a' the two > character raw form by means of escaping \ ( and raises a KeyError > exception otherwise ).
>>>>c = '\a' >>>>print rawform(c)
> \a
> This has the same effect as writing:
>>>>c = r'\a' >>>>print c
> \a
> But there is some ambiguity due to the the fact that applying '\7' to > rawform() yields r'\a' and not r'\7'. So one needs more specification > for disambiguation using e.g. an extra parameter.
In [33]: "\7" == "\a" Out[33]: True
Sorry. It can't possibly know which of two alternative representation were used to represent a particular character in a literal.
>>> Usually I struggle a short while with \ and either succeed or give up. >>> Today I'm in a different mood and don't give up. So here is my >>> question:
>>> You have an unknown character string c such as '\n' , '\a' , '\7' etc.
>>> How do you echo them using print?
>>> print_str( c ) prints representation '\a' to stdout for c = '\a' >>> print_str( c ) prints representation '\n' for c = '\n' >>> ...
>>> It is required that not a beep or a linebreak shall be printed.
>> try "print repr(c)".
> This yields the hexadecimal representation of the ASCII character and > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > escape semantics. One way to achieve this naturally is by prefixing > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > "rawrification" applies only to string literals and not to string > objects ( such as c ). I consider creating a table consisting of pairs > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > I've overlooked some simple function or trick that does the same for > me.
> Kay
Kay,
This is perhaps yet another case for SE? I don't really know, because I don't quite get what you're after. See for yourself:
>>> import SE >>> Printabilizer = SE.SE ( ''' (1)=\\1 # All 256 octets can be written as parenthesized ascii (2)=\\2 "\a=\\a" # (7)=\\a" "\n=\\n" # or (10)=\\n or (10)=LF or whatever "\r=\\r" # (13)=CR "\f=\\f" "\v=\\v" # Add whatever other ones you like # and translate them to anything you like. ''')
> >>> Usually I struggle a short while with \ and either succeed or give up. > >>> Today I'm in a different mood and don't give up. So here is my > >>> question:
> >>> You have an unknown character string c such as '\n' , '\a' , '\7' etc.
> >>> How do you echo them using print?
> >>> print_str( c ) prints representation '\a' to stdout for c = '\a' > >>> print_str( c ) prints representation '\n' for c = '\n' > >>> ...
> >>> It is required that not a beep or a linebreak shall be printed.
> >> try "print repr(c)".
> > This yields the hexadecimal representation of the ASCII character and > > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > > escape semantics. One way to achieve this naturally is by prefixing > > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > > "rawrification" applies only to string literals and not to string > > objects ( such as c ). I consider creating a table consisting of pairs > > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > > I've overlooked some simple function or trick that does the same for > > me.
> > Kay
> Kay,
> This is perhaps yet another case for SE? I don't really know, because I > don't quite get what you're after. See for yourself:
> >>> import SE > >>> Printabilizer = SE.SE ( ''' > (1)=\\1 # All 256 octets can be written as parenthesized ascii > (2)=\\2 > "\a=\\a" # (7)=\\a" > "\n=\\n" # or (10)=\\n or (10)=LF or whatever > "\r=\\r" # (13)=CR > "\f=\\f" > "\v=\\v" > # Add whatever other ones you like > # and translate them to anything you like. > ''')
This looks quite good. "rawrification" or "printabalization" that's exactly what I was looking for and I thought this problem would be so common that someone has done an implementation already. Thanks, Frederik!
"Kay Schluehr" <kay.schlu...@gmx.net> wrote: > Sybren Stuvel wrote: > > Kay Schluehr enlightened us with: > > > Usually I struggle a short while with \ and either succeed or give up. > > > Today I'm in a different mood and don't give up. So here is my > > > question:
> > > You have an unknown character string c such as '\n' , '\a' , '\7' etc.
> > > How do you echo them using print?
> > > print_str( c ) prints representation '\a' to stdout for c = '\a' > > > print_str( c ) prints representation '\n' for c = '\n' > > > ...
> > > It is required that not a beep or a linebreak shall be printed.
> > try "print repr(c)".
> This yields the hexadecimal representation of the ASCII character and > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > escape semantics. One way to achieve this naturally is by prefixing > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > "rawrification" applies only to string literals and not to string > objects ( such as c ). I consider creating a table consisting of pairs > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > I've overlooked some simple function or trick that does the same for > me.
> Kay
dumb question - is the backslash as escape character fixed or can one set its (the escape char's) value so that backslash is not the escape char?
seems to me that would help - or if you could turn the behaviour off - don't know how though...
Kay Schluehr wrote: > This yields the hexadecimal representation of the ASCII character and > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > escape semantics. One way to achieve this naturally is by prefixing > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > "rawrification" applies only to string literals and not to string > objects ( such as c ). I consider creating a table consisting of pairs > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > I've overlooked some simple function or trick that does the same for > me.
if not else, you've missed that octal escapes consists of three digits, not one, so translating chr(1) to r"\1" doesn't work in the general case (e.g. len("\100") == 1, not 3)
> -----Original Message----- > From: > python-list-bounces+matthew.warren=digica....@python.org > [mailto:python-list-bounces+matthew.warren=digica....@python.o > rg] On Behalf Of Kay Schluehr > Sent: 30 September 2006 18:02 > To: python-l...@python.org > Subject: Re: Escapeism
> Sybren Stuvel wrote: > > Kay Schluehr enlightened us with: > > > Usually I struggle a short while with \ and either > succeed or give up. > > > Today I'm in a different mood and don't give up. So here is my > > > question:
> > > You have an unknown character string c such as '\n' , > '\a' , '\7' etc.
> > > How do you echo them using print?
> > > print_str( c ) prints representation '\a' to stdout for c = '\a' > > > print_str( c ) prints representation '\n' for c = '\n' > > > ...
> > > It is required that not a beep or a linebreak shall be printed.
> > try "print repr(c)".
> This yields the hexadecimal representation of the ASCII character and > does not simply echo the keystrokes '\' and 'a' for '\a' ignoring the > escape semantics. One way to achieve this naturally is by prefixing > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > "rawrification" applies only to string literals and not to string > objects ( such as c ). I consider creating a table consisting of pairs > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > I've overlooked some simple function or trick that does the same for > me.
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> -----Original Message----- > From: > python-list-bounces+matthew.warren=digica....@python.org > [mailto:python-list-bounces+matthew.warren=digica....@python.o > rg] On Behalf Of Matthew Warren > Sent: 03 October 2006 16:07 > To: python-l...@python.org > Subject: RE: Escapeism
> > -----Original Message----- > > From: > > python-list-bounces+matthew.warren=digica....@python.org > > [mailto:python-list-bounces+matthew.warren=digica....@python.o > > rg] On Behalf Of Kay Schluehr > > Sent: 30 September 2006 18:02 > > To: python-l...@python.org > > Subject: Re: Escapeism
> > Sybren Stuvel wrote: > > > Kay Schluehr enlightened us with: > > > > Usually I struggle a short while with \ and either > > succeed or give up. > > > > Today I'm in a different mood and don't give up. So here is my > > > > question:
> > > > You have an unknown character string c such as '\n' , > > '\a' , '\7' etc.
> > > > How do you echo them using print?
> > > > print_str( c ) prints representation '\a' to stdout for c = '\a' > > > > print_str( c ) prints representation '\n' for c = '\n' > > > > ...
> > > > It is required that not a beep or a linebreak shall be printed.
> > > try "print repr(c)".
> > This yields the hexadecimal representation of the ASCII > character and > > does not simply echo the keystrokes '\' and 'a' for '\a' > ignoring the > > escape semantics. One way to achieve this naturally is by prefixing > > '\a' with r where r'\a' indicates a "raw" string. But unfortunately > > "rawrification" applies only to string literals and not to string > > objects ( such as c ). I consider creating a table > consisting of pairs > > {'\0': r'\0','\1': r'\1',...} i.e. a handcrafted mapping but maybe > > I've overlooked some simple function or trick that does the same for > > me.
> > Kay
((I have no idea why the following was missing from my first attempt to post, and since posting the thread has gone over my head, but wasn't the OP just after a way to print user-inputted strings with '\' in them?))...
I cant test this where I am, but would the following work
We have our literal user-inputted strings in a list,
l=['\a','\b','\c'] etc..
For s in l: for c in s: print c, print
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