Update column attributes dynamically in Python?

Question

I have a table where I'm trying to create the value of the attribute from one column based off the attribute of the value of another column...

Essentially, one column is a long series of numbers... such as 540379724021081 and I am trying to for that tuple, make another attribute value of the first 4 characters so...5403

So in the end my table would go from...

To this...

I started doing this in Python with Psycopg2...but don't think it's the right way with a quick script I made

import psycopg2

conn = psycopg2.connect("dbname='gis3capstone' user='postgres' password='password' host='localhost' port='5433'")
cur = conn.cursor()

cur.execute('SELECT * FROM fcc_form_477')
row = cur.fetchone()
while row:
    val2 = str(row[0])[0:4]
    # Set row[1] = val2 ??
    row = cur.fetchone()

Any help to go about this?

EDIT: or SQL...if I can do it that way

Gordon Linoff · Accepted Answer · 2018-04-18 01:44:22Z

1

You can use substr():

select substr(val1, 1, 4) as val2

If the value is a number, then convert it to a string:

select substr(val1::text, 1, 4) as val2

answered Apr 18, 2018 at 1:44

Gordon Linoff

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