Write data in file using python

Question

I'm working on a python project and I want to write some data in a file text.txt but I have this error : UnboundLocalError: local variable 'data' referenced before assignment This is my code :

from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/', methods=['POST','GET'])
def createapp():
    if request.method == 'POST':
        data = request.json
        print(data)
        
    with open('text.txt', 'a') as file:
        file.write(data)


if __name__ =='__main__':
    app.run()

FLAK-ZOSO · Accepted Answer · 2022-05-21 15:29:58Z

3

if request.method == 'POST':
    data = request.json
    print(data)
    
with open('text.txt', 'a') as file:
    file.write(data)

And what if request.method != 'POST'? You won't have defined data.

If you want to add something new (maybe a 0 or a []) when data is null, you may want to add this before the if statement:

data = ''

edited May 21, 2022 at 15:29

answered May 21, 2022 at 15:00

FLAK-ZOSO

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2 Comments

beatfloraminederecho Over a year ago

I'm new to python I just want to add those data in the file text.txt

Liron Berger Over a year ago

Small correction - data = '', otherwise TypeError will be raised

Mohammad Rifat Arefin · Accepted Answer · 2022-05-21 15:07:32Z

2

Set data to empty string before the condition. Otherwise it's undefined if the condition is false

data=''
if request.method == 'POST':
    data = request.json
    print(data)
    
with open('text.txt', 'a') as file:
    file.write(data)

edited May 21, 2022 at 15:07

answered May 21, 2022 at 15:03

Mohammad Rifat Arefin

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7 Comments

Liron Berger Over a year ago

Actually you will raise a TypeError here, because you must write a string to file. data = '' will fix it

beatfloraminederecho Over a year ago

thank you but the data is null I want to write in my file the data = request.json

Mohammad Rifat Arefin Over a year ago

You can write into the file within the if block. In that case, you don't need to declare data beforehand.

beatfloraminederecho Over a year ago

If I write it inside the if block it didn't show in the text.txt

Mohammad Rifat Arefin Over a year ago

So you are saying data is printed on terminal but not written into the text.txt file? Check what's printed on terminal.

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