for loop in flask python

Question

i have this simple for loop in flask framework

@app.route('/kde')
def fetch_erga():
    cur = mysql.connection.cursor()
    cur.execute("SELECT ergo FROM erga")
    rv = list(cur.fetchall())
    for row in rv:
        stock = str(row[0]['ergo'])
        tsapr += [(stock)]
    return '<h2>' + tsapr + '</h2>'

This leads to jinja crashing and producing the following error in the browser: KeyError: 0

is it an error with key evaluation or the lack of it, or is it just bad looping? Any help would be aprreciated

edit: when running this:

@app.route('/kdef')
def fetch_ergas():
    cur = mysql.connection.cursor()
    cur.execute("SELECT ergo FROM erga")
    rv = list(cur.fetchall())
    return '<h2>' + str(rv) + '</h2>'

i get the following results in the browser

[{'ergo': u'52018'}, {'ergo': u'52019'}, {'ergo': u'63096700'}, {'ergo': u'68003400'}, {'ergo': u'68003501'}, {'ergo': u'69003501'}]

I mean it is not an empty cursor

marc_s · Accepted Answer · 2018-11-14 20:51:18Z

1

KeyError is usually associated with a missing key in a dictionary. If it were me I would start looking into str(row[0]['ergo']). Is it possible one of the row objects in rv does not have 'ergo' key?

maybe if cur.execute("SELECT ergo FROM erga") returns an empty queryset?

EDIT:

every row in rv is a dict type object and you're referencing row[0] but there is no 0 key, change stock = str(row[0]['ergo']) to be stock = str(row['ergo']) and it should work

edited Nov 14, 2018 at 20:51

marc_s

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answered Nov 9, 2018 at 12:38

vencaslac

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5 Comments

manosv Over a year ago

thx for your answer. running this: @app.route('/tyropitta') def tyri(): cur = mysql.connection.cursor() cur.execute('SELECT ergo from erga') rv = list(cur.fetchall()) #lista #return '<h1>' + str(rv[0]['ergo']) + '</h1>' return '<h1>' + str(rv) + '</h1>' gives me the following list [{'ergo': u'52018'}, {'ergo': u'52019'}, {'ergo': u'63096700'}, {'ergo': u'68003400'}, {'ergo': u'68003501'}, {'ergo': u'69003501'}]. So the selection cursor is not empty...

manosv Over a year ago

[{'ergo': u'52018'}, {'ergo': u'52019'}, {'ergo': u'63096700'}, {'ergo': u'68003400'}, {'ergo': u'68003501'}, {'ergo': u'69003501'}]

manosv Over a year ago

@app.route('/tyropitta') def tyri():     cur = mysql.connection.cursor()     cur.execute('SELECT ergo from erga')     rv = list(cur.fetchall()) #lista     #return '<h1>' + str(rv[0]['ergo']) + '</h1>'     return '<h1>' + str(rv) + '</h1>'

vencaslac Over a year ago

try editing your question instead of commenting, its' not very legible

manosv Over a year ago

Worked like a charm! :)

Marcos Stefani Rosa · Accepted Answer · 2018-11-10 14:30:51Z

1

You'd better use the template engine itself for this: http://jinja.pocoo.org/docs/2.10/templates/#block-nesting-and-scope

answered Nov 10, 2018 at 14:30

Marcos Stefani Rosa

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