RegEx Pattern Matching

#ENCODING
import io
import sys
sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding='utf-16')
#MONGO
from pymongo import MongoClient
client = MongoClient()
client.progzoo.authenticate('scott','tiger')
db = client['progzoo']
#PRETTY
import pprint
pp = pprint.PrettyPrinter(indent=4)

Pattern Matching String

This tutorial uses RegEx to check names. We will be using find() on the collection world.

You can use '$regex':"^B" to get all the countries that start with B.

Find the countries that start with Y

pp.pprint(list(
    db.world.find({"name":{'$regex':"^F"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"^Y"}},{"name":1,"_id":0})))

You can use '$regex':"a$" to get all the countries that end with a.

Find the countries that end with Y

pp.pprint(list(
    db.world.find({"name":{'$regex':"l$"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"y$"}},{"name":1,"_id":0})))

Luxembourg has an x, so does one other country, list them both

Find the countries that contain the letter x

pp.pprint(list(
    db.world.find({"name":{'$regex':"ana"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"x"}},{"name":1,"_id":0})))

Iceland and Switzerland end with land but where are the others?

Find the countries that end with land

pp.pprint(list(
    db.world.find({"name":{'$regex':"stan$"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"land$"}},{"name":1,"_id":0})))

Columbia starts with a C and ends with ia - there are two other countries like this.
You can use .* to match any character except newlines.

Find the countries that start with C and end with ia

pp.pprint(list(
    db.world.find({"name":{'$regex':"^A.*n$"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"^C.*ia$"}},{"name":1,"_id":0})))

Greece has a double e, who has a double o

Find the countty that has oo in its name

pp.pprint(list(
    db.world.find({"name":{'$regex':"ee"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"oo"}},{"name":1,"_id":0})))

Bahamas has three a, who else?

Find the country that has three or more a in the name

pp.pprint(list(
    db.world.find({"name":{'$regex':"^T"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"(.*[aA].*){3}"}},{"name":1,"_id":0})))

India and Angola have n as their second character.
.* Indicates one or more characters, . indicates just one.

Find the countries that have "t" as the second character.

pp.pprint(list(
    db.world.find({"name":{'$regex':"^.n"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"^.t"}},{"name":1,"_id":0})))

Lesotho and Moldova both have two o characters seperated by two other characters.

Find the countries that have two "o" characters separated by two others.

pp.pprint(list(
    db.world.find({"name":{'$regex':"o.o"}},{"name":1,"_id":0})
))

pp.pprint(list(db.world.find({"name":{'$regex':"o..o"}},{"name":1,"_id":0})))