[Tutor] referencing a dictionary

Daniel Yoo dyoo@hkn.EECS.Berkeley.EDU
Mon, 17 Jul 2000 13:25:40 -0700 (PDT)

On Mon, 17 Jul 2000, brian callahan wrote:

>   my idea is to use a raw_input string, to search a dictionary that contains 
> all the characters in the raw_input string with a value, and then i want to 
> sum the values.  my script is used to take a the amino acid sequence of a 
> protein and then give back the molecular weight.  i've been using the 
> 'learning python' book but im getting impatient.

Can you give an example of what sort of input you're going to parse out of

I'll assume that you're already familiar with dictionaries from another
language.  As a crash course, here are some the basic operations on
dictionaries ("hashtables"):

Creating an empty hashtable:

  myhash = {}

Creating a hashtable with initial entries:

  myhash = {'tryptophan' : 0.3, 'lysine': 0.44, 'methionine': 0.76}

Looking up an entry, given a known key:


Adding a new key/value pair into a dictionary:

  myhash['glutamic acid'] = 0.90

Getting all the keys as a list:


Checking if a key exists in the hash:

  if myhash.has_key('tyrosine'):  ...

With these, you should be able to use dictionaries productively.  If you
have any questions, or would like to see an extended example, just email
tutor@python.org again.  Good luck!