Is Python Suitable for Large Find & Replace Operations?

[John Machin]

rbt wrote:
> Here's the scenario:
> 
> You have many hundred gigabytes of data... possible even a terabyte or 
> two. Within this data, you have private, sensitive information (US 
> social security numbers) about your company's clients. Your company has 
> generated its own unique ID numbers to replace the social security numbers.
> 
> Now, management would like the IT guys to go thru the old data and 
> replace as many SSNs with the new ID numbers as possible.

This question is grossly OT; it's nothing at all to do with Python. 
However ....

(0) Is this homework?

(1) What to do with an SSN that's not in the map?

(2) How will a user of the system tell the difference between "new ID 
numbers" and SSNs?

(3) Has the company really been using the SSN as a customer ID instead 
of an account number, or have they been merely recording the SSN as a 
data item? Will the "new ID numbers" be used in communication with the 
clients? Will they be advised of the new numbers? How will you handle 
the inevitable cases where the advice doesn't get through?

(4) Under what circumstances will it not be possible to replace *ALL* 
the SSNs?

(5) For how long can the data be off-line while it's being transformed?


> You have a tab 
> delimited txt file that maps the SSNs to the new ID numbers. There are 
> 500,000 of these number pairs.

And what is the source of the SSNs in this file??? Have they been 
extracted from the data? How?

> What is the most efficient way  to 
> approach this? I have done small-scale find and replace programs before, 
> but the scale of this is larger than what I'm accustomed to.
> 
> Any suggestions on how to approach this are much appreciated.

A sensible answer will depend on how the data is structured:

1. If it's in a database with tables some of which have a column for 
SSN, then there's a solution involving SQL.

2. If it's in semi-free-text files where the SSNs are marked somehow:

---client header---
surname: Doe first: John initial: Q SSN:123456789 blah blah
or
<ssn>123456789</ssn>

then there's another solution which involves finding the markers ...

3. If it's really free text, like
"""
File note: Today John Q. Doe telephoned to advise that his Social 
Security # is 123456789  not 987654321 (which is his wife's) and the soc 
sec numbers of his kids Bob & Carol are ....
"""
then you might be in some difficulty ... google("TREC")


AND however you do it, you need to be very aware of the possibility 
(especially with really free text) of changing some string of digits 
that's NOT an SSN.

HTH,
John