Mailing List Archive: Help with dictionary, please

Help with dictionary, please

Aug 6, 1999, 5:21 AM

Post #1 of 8 (1048 views)

I'm rapidly trying to learn Python and despite reading the documentation
and the "Learning Python" book, I can't figure out how to do the following:

- I want to have a 2-dimensional array of word counts, indexed by
a pair of words. I.e. dict[word1,word2]
- In C, I'd just create a 2-dimensional array of integers and increment
as required, but would have to hash the words into integer indices.

- I tried the following in Python:
dict = {}
prev1 = ''
prev2 = ''
[snip]

if prev1 != '' and prev2 != '':
key = (prev2,prev1)
dict[key] = dict[key] + 1
and got this error:
File "Metro:Python 1.5.1:learn2.py", line 34
dict[key] = dict[key] + 1
^
SyntaxError: invalid token

I'm obviously missing something here!

Any guidance greatly appreciated!

Thank you,
Rob Lake
rbl@hal.cwru.edu

Help with dictionary, please [ In reply to ]

frankn=news at cs

Aug 6, 1999, 5:32 AM

Post #2 of 8 (1038 views)

Permalink

rbl@hal.cwru.edu wrote:
> if prev1 != '' and prev2 != '':
> key = (prev2,prev1)
> dict[key] = dict[key] + 1
> and got this error:
> File "Metro:Python 1.5.1:learn2.py", line 34
> dict[key] = dict[key] + 1
> ^
> SyntaxError: invalid token

You need to initialize the value at dict[key], it is not automatically
set to 0 or something like that. For example:

if dict.has_key(key):
dict[key] = dict[key] + 1
else:
dict[key] = 1

However, you should've got a KeyError, I don't understand why you're
getting the SyntaxError...

HTH, Frank

--
He went across to the telephone machine and fiddled and fumed with all its
buttons for a while, because it was the one which was particularly recom-
mended by Which? magazine and is almost impossible to use without going mad.
-- Douglas Adams, 'So long, and thanks for all the fish'

AW: Help with dictionary, please [ In reply to ]

Delius at ebox

Aug 6, 1999, 5:36 AM

Post #3 of 8 (1040 views)

Permalink

Hi Rob,

I tried the example and it worked for me. Maybe it's just a problem of
indentication, because the last two lines in Your example should be indentet
at the same level and you indented two more spaces in front of
'dict[key]...' ?!?

> if prev1 != '' and prev2 != '':
> key = (prev2,prev1)
> dict[key] = dict[key] + 1

Or You're mixing spaces and tabs?!? Just a guess...

-Felix
---
Dipl.-Ing. Felix von Delius Fon: 0911/4244-110
Projektleiter-IT Fax: 0911/4244-100
EBox GmbH - Agentur für neue Medien Mobil: 0172/8261220
Vordere Cramergasse 11 Email: delius@ebox.de
D-90425 Nuernberg Web: http://www.ebox.de

Help with dictionary, please [ In reply to ]

phd at emerald

Aug 6, 1999, 5:38 AM

Post #4 of 8 (1043 views)

Permalink

On 6 Aug 1999 rbl@hal.EPBI.CWRU.Edu wrote:
> key = (prev2,prev1)
> dict[key] = dict[key] + 1
> and got this error:
> File "Metro:Python 1.5.1:learn2.py", line 34
> dict[key] = dict[key] + 1
> ^
> SyntaxError: invalid token
>
> I'm obviously missing something here!

You messed tabs and spaces. Make all things tabs or spaces, but do not
use both.

Advice N2:
The line
dict[key] = dict[key] + 1
will cause troubles, if key not in dict. You better write it the
following way:
dict[key] = dict.get(key, 0) + 1

dict.get is a function that returns either value for the key or default,
if the key not in the dictionary.

> Any guidance greatly appreciated!
>
> Thank you,
> Rob Lake
> rbl@hal.cwru.edu

Oleg.
----
Oleg Broytmann Netskate/Inter.Net.Ru phd@emerald.netskate.ru
Programmers don't die, they just GOSUB without RETURN.

Help with dictionary, please [ In reply to ]

kas at maps

Aug 6, 1999, 5:51 AM

Post #5 of 8 (1037 views)

Permalink

Rob Lake writes:

> key = (prev2,prev1)
> dict[key] = dict[key] + 1
> and got this error:
> File "Metro:Python 1.5.1:learn2.py", line 34
> dict[key] = dict[key] + 1
> ^
> SyntaxError: invalid token

The variable key should be a string, you're supplying a tupple.

//Klaus

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Help with dictionary, please [ In reply to ]

kajiyama at grad

Aug 6, 1999, 7:04 AM

Post #6 of 8 (1041 views)

Permalink

rbl@hal.cwru.edu writes:
|
| if prev1 != '' and prev2 != '':
| key = (prev2,prev1)
| dict[key] = dict[key] + 1
| and got this error:
| File "Metro:Python 1.5.1:learn2.py", line 34
| dict[key] = dict[key] + 1
| ^
| SyntaxError: invalid token
|
| I'm obviously missing something here!

What you do seems good to me. I wonder if you have trouble with white
space, since the code snippet shown above contains both space and tab
characters.

White space characters in indentation make sense in Python. To avoid
mysterious syntax error, you'd better use either space or tab
characters, and not mix them.

Regards,

--
KAJIYAMA, Tamito <kajiyama@grad.sccs.chukyo-u.ac.jp>

Help with dictionary, please [ In reply to ]

gmcm at hypernet

Aug 6, 1999, 7:13 AM

Post #7 of 8 (1043 views)

Permalink

Klaus Alexander Seistrup wrote:

> The variable key should be a string, you're supplying a tupple.

Not at all. Tuples (or any immutable object) make fine dictionary
keys.

The original problem is almost undoubtedly indentation (tabs &
spaces, with editor interpretation out of sync with Python's).

- Gordon

Help with dictionary, please [ In reply to ]

kas at maps

Aug 6, 1999, 9:15 AM

Post #8 of 8 (1036 views)

Permalink

Gordon McMillan wrote:

> > The variable key should be a string, you're supplying a tupple.
>
> Not at all. Tuples (or any immutable object) make fine dictionary
> keys.

Sure, I was confusing dictionaries with anydbm objects. I even tried to
cancel my article but it seems that you were too fast. ;-) Sorry about
the misinformation.

> The original problem is almost undoubtedly indentation (tabs &
> spaces, with editor interpretation out of sync with Python's).

Yes, I read your answer.

Cheers,

//Klaus

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