Re: String formatting with the format string syntax

2010-09-15 Thread Peter Otten 
Andre Alexander Bell wrote:

 On 09/14/2010 08:20 PM, Miki wrote:
 You can use ** syntax:
 english = {'hello':'hello'}
 s.format(**english)
 
 Thanks for your answer. Actually your answer tells me that my example
 was misleading. Consider the template
 
 s = 'A template with {variable1} and {variable2} placeholders.'
 
 I'm seeking a way to extract the named placesholders, i.e. the names
 'variable1' and 'variable2' from the template. I'm not trying to put in
 values for them.
 
 I hope this is clearer.

 s = 'A template with {variable1} and {variable2} placeholders.'
 [name for _, name, _, _ in s._formatter_parser() if name is not None]
['variable1', 'variable2']

Peter
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Re: String formatting with the format string syntax

2010-09-15 Thread Peter Otten 
Peter Otten wrote:

 Andre Alexander Bell wrote:
 
 On 09/14/2010 08:20 PM, Miki wrote:
 You can use ** syntax:
 english = {'hello':'hello'}
 s.format(**english)
 
 Thanks for your answer. Actually your answer tells me that my example
 was misleading. Consider the template
 
 s = 'A template with {variable1} and {variable2} placeholders.'
 
 I'm seeking a way to extract the named placesholders, i.e. the names
 'variable1' and 'variable2' from the template. I'm not trying to put in
 values for them.
 
 I hope this is clearer.
 
 s = 'A template with {variable1} and {variable2} placeholders.'
 [name for _, name, _, _ in s._formatter_parser() if name is not None]
 ['variable1', 'variable2']

Caveat: the format spec may contain names, too. 
Here's an attempt to take that into account:

def extract_names(t, recurse=1):
for _, name, fmt, _ in t._formatter_parser():
if name is not None:
yield name
if recurse and fmt is not None:
for name in extract_names(fmt, recurse-1):
yield name

t = before {one:{two}{three}} after
print(t)

for name in extract_names(t):
print(name)

 list(extract_names({one:{two}{three}}))
['one', 'two', 'three']

Don't expect correct results for illegal formats:
 list(extract_names({one:{two:{three}}}))
['one', 'two']
 {one:{two:{three}}}.format(one=1, two=2, three=3)
Traceback (most recent call last):
  File stdin, line 1, in module
ValueError: Max string recursion exceeded

Duplicate names may occur:
 list(extract_names({one} {one} {one}))
['one', 'one', 'one']

Positional arguments are treated like names:
 list(extract_names({0} {1} {0}))
['0', '1', '0']
 list(extract_names({} {} {}))
['', '', '']

Peter
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Re: String formatting with the format string syntax

2010-09-15 Thread Andre Alexander Bell 

On 09/15/2010 10:00 AM, Peter Otten wrote:

def extract_names(t, recurse=1):
 for _, name, fmt, _ in t._formatter_parser():
 if name is not None:
 yield name
 if recurse and fmt is not None:
 for name in extract_names(fmt, recurse-1):
 yield name


Thanks Peter, I very much like this generator solution. It will work for 
all situations I can currently think of.


However, one thing remains. It is based on the _format_parser method. 
And as I wrote in my original post this one - since it starts with _ - 
suggests to me to better not be used. So if using this method is 
completely ok, why does it start with _, why is it almost undocumented? 
Or did I miss something, some docs somewhere?


Best regards


Andre

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Re: String formatting with the format string syntax

2010-09-15 Thread Peter Otten 
Andre Alexander Bell wrote:

 On 09/15/2010 10:00 AM, Peter Otten wrote:
 def extract_names(t, recurse=1):
  for _, name, fmt, _ in t._formatter_parser():
  if name is not None:
  yield name
  if recurse and fmt is not None:
  for name in extract_names(fmt, recurse-1):
  yield name
 
 Thanks Peter, I very much like this generator solution. It will work for
 all situations I can currently think of.
 
 However, one thing remains. It is based on the _format_parser method.
 And as I wrote in my original post this one - since it starts with _ -
 suggests to me to better not be used. So if using this method is
 completely ok, why does it start with _, why is it almost undocumented?
 Or did I miss something, some docs somewhere?

Sorry, I really should have read your original post carefully/completely. It 
would have spared me from finding _formatter_parser() independently...

I personally would not be too concerned about the leading underscore, but 
you can use

string.Formatter().parse(template)

instead.

Peter

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Re: String formatting with the format string syntax

2010-09-15 Thread Andre Alexander Bell 

On 09/15/2010 10:48 AM, Peter Otten wrote:

I personally would not be too concerned about the leading underscore, but
you can use

string.Formatter().parse(template)

instead.


Thanks for this pointer. I like it this way. So if I now combine your 
generator with your suggestion, I end up with something like this:


def extract_names(t, recurse=1):
import string
for _, name, fmt, _ in string.Formatter().parse(t):
if name is not None:
yield name
if recurse and fmt is not None:
for name in extract_names(fmt, recurse-1):
yield name

Pretty cool. Thanks a lot.

Andre
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Re: String formatting with the format string syntax

2010-09-14 Thread Miki 
You can use ** syntax:
 english = {'hello':'hello'}
 s.format(**english)

On Sep 14, 9:59 am, Andre Alexander Bell p...@andre-bell.de wrote:
 Hello,

 I'm used to write in Python something like

   s = 'some text that says: %(hello)s'

 and then have a dictionary like

   english = { 'hello': 'hello' }

 and get the formatted output like this:

   s % english

 Occasionally I want to extract the field names from the template string.
 I was used to write a class like

 class Extractor(object):
      def __init__(self):
          self.keys = []
      def __getitem__(self, key):
          self.keys.append(key)
          return ''

 and use it like this:

   e = Extractor()
   res = s % e
   e.keys
 ['hello']

 Now Python has the format method for string formatting with the more
 advanced handling. So I could as well write

   s = 'some text that says: {hello!s}'
   s.format(hello='hello')

 My question is, if I do have a string template which uses the newer
 format string syntax, how do I best extract the field information?

 I found the str._formatter_parser() method which I could use like this:

 keys = []
 for (a, key, c, d) in s._formatter_parser():
      if key:
          keys.append(key)

 Is there a more elegant solution?
 What are a, c, d?
 Where can I find additional information on this method?
 Should one use a method that actually starts with an _?
 Couldn't this one change any time soon?

 Thanks for any help

 Andre

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Re: String formatting with the format string syntax

2010-09-14 Thread Thomas Jollans 
On Tuesday 14 September 2010, it occurred to Miki to exclaim:
 You can use ** syntax:
  english = {'hello':'hello'}
  s.format(**english)

No, you can't. This only works with dicts, not with arbitrary mappings, or 
dict subclasses that try to do some kind of funny stuff. 

 
 On Sep 14, 9:59 am, Andre Alexander Bell p...@andre-bell.de wrote:
  Hello,
  
  I'm used to write in Python something like
  
s = 'some text that says: %(hello)s'
  
  and then have a dictionary like
  
english = { 'hello': 'hello' }
  
  and get the formatted output like this:
  
s % english
  
  Occasionally I want to extract the field names from the template string.
  I was used to write a class like
  
  class Extractor(object):
   def __init__(self):
   self.keys = []
   def __getitem__(self, key):
   self.keys.append(key)
   return ''
  
  and use it like this:
  
e = Extractor()
res = s % e
e.keys
  ['hello']
  
  Now Python has the format method for string formatting with the more
  advanced handling. So I could as well write
  
s = 'some text that says: {hello!s}'
s.format(hello='hello')
  
  My question is, if I do have a string template which uses the newer
  format string syntax, how do I best extract the field information?
  
  I found the str._formatter_parser() method which I could use like this:
  
  keys = []
  for (a, key, c, d) in s._formatter_parser():
   if key:
   keys.append(key)
  
  Is there a more elegant solution?
  What are a, c, d?
  Where can I find additional information on this method?
  Should one use a method that actually starts with an _?
  Couldn't this one change any time soon?
  
  Thanks for any help
  
  Andre
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Re: String formatting with the format string syntax

2010-09-14 Thread Benjamin Kaplan 
On Tue, Sep 14, 2010 at 3:20 PM, Thomas Jollans tho...@jollybox.de wrote:
 On Tuesday 14 September 2010, it occurred to Miki to exclaim:
 You can use ** syntax:
  english = {'hello':'hello'}
  s.format(**english)

 No, you can't. This only works with dicts, not with arbitrary mappings, or
 dict subclasses that try to do some kind of funny stuff.


That was changed in 2.6
http://docs.python.org/release/2.6.6/whatsnew/2.6.html#other-language-changes
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Re: String formatting with the format string syntax

2010-09-14 Thread Andre Alexander Bell 

On 09/14/2010 08:20 PM, Miki wrote:

You can use ** syntax:

english = {'hello':'hello'}
s.format(**english)


Thanks for your answer. Actually your answer tells me that my example 
was misleading. Consider the template


s = 'A template with {variable1} and {variable2} placeholders.'

I'm seeking a way to extract the named placesholders, i.e. the names 
'variable1' and 'variable2' from the template. I'm not trying to put in 
values for them.


I hope this is clearer.

Thanks again


Andre

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