Extracting numbers from a string in Python

Question

When I query my MySQL Database I get some extra characters that I don't want. For example, instead of getting 165 I get (165), so, I tried the following in order to extract the number.

The problem is that instead of getting only the number, my code will print nothing, I can't find the reason. Any advice?

 arr = ''

    num = re.findall('\d+', arr)

    mydb = mysql.connector.connect(
        host="localhost",
        user="root",
        database="diff"
    )

    mycursor = mydb.cursor()

    mycursor.execute("SELECT * FROM val ORDER BY num DESC LIMIT 1")
    myresult = mycursor.fetchall()

    for x in myresult:
        arr = x        
        print(arr)

It seems that myresult is empty. Use a debugger or print statements to see which statements are being executed. — roeen30
– roeen30, Commented Nov 17, 2018 at 20:52
Also the first 2 lines are strange. num will be empty is not used. You maybe want to use the compile method in re to create a regex object. e.g. pattern = re.compile("\d+") and call pattern.findall(x) in the loop. — ramin
– ramin, Commented Nov 17, 2018 at 20:54

ramin · Accepted Answer · 2018-11-17 20:58:59Z

2

something like this maybe:

mydb = mysql.connector.connect(
    host="localhost",
    user="root",
    passwd="Bellini10-",
    database="diff"
)

mycursor = mydb.cursor()

mycursor.execute("SELECT * FROM val ORDER BY num DESC LIMIT 1")
myresult = mycursor.fetchall()

pattern = re.compile("\d+") 

for x in myresult:
    num = pattern.findAll(x)[0]       
    print(num)

answered Nov 17, 2018 at 20:58

ramin

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1 Comment

Dev012 Over a year ago

I did not think about it. Thanks for answering!

Sam Mason · Accepted Answer · 2018-11-17 21:56:21Z

1

most Python database connectors I've used give back tuples, you'd thus want to do:

for (x,) in myresult:
  print(x)

and you should get what you want

the docs I get suggest you can also just the cursor an iterable context manager, thus something like:

with mydb.cursor() as cur:
  cur.execute("SELECT * FROM val ORDER BY num DESC LIMIT 1")
  for (x,) in cur:
    print(x)

would be more idiomatic Python

edited Nov 17, 2018 at 21:56

answered Nov 17, 2018 at 21:50

Sam Mason

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1 Comment

Dev012 Over a year ago

This makes sense. Thanks!

Om A. · Accepted Answer · 2018-11-17 20:55:40Z

1

Try this:

whitelist = set('0123456789')
num = ''.join(filter(whitelist.__contains__, arr))

Hope this helps!

answered Nov 17, 2018 at 20:55

Om A.

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1 Comment

Om A. Over a year ago

No problem - glad I could help!

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