Transform an Uploaded CSV File Upload with Flask

I have a simple Flask app hosted on Python Anywhere. The app provides an interface where a user can upload a CSV file, and the app inserts a new column into the uploaded CSV file by overwriting the first column (row[0]) and putting the original row[0] at the end of the file and downloads the transformed file for the user. So, the CSV input looks like this (first row is a header row that should be unmodified save for the addition of a 4th column name):

Pet1,Pet2,Pet3
Cats,Dogs,Mice

And the output should look like:

Pet1,Pet2,Pet3,Pet4
Birds,Dogs,Mice,Cats

Here is my code:

from flask import Flask, make_response, request
import operator
import io
import csv

app = Flask(__name__)

def transform(text_file_contents):
 reader = csv.reader(text_file_contents)
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0))
 return sortedlist


@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 if not request_file:
 return "No file"

file_contents = request_file.stream.read().decode("utf-8")

result = transform(file_contents)

response = make_response(result)
response.headers["Content-Disposition"] = "attachment; filename=result.csv"
return response

This is the error I am getting:

Traceback (most recent call last):
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/user/mysite/callnumbers.py", line 62, in transform_view
result = transform(file_contents)
File "/home/user/mysite/callnumbers.py", line 18, in transform
row[0] = row[1]
IndexError: list index out of range

I can tell that my script isn't reading the uploaded input file correctly (hence not being able to find the data in the columns I am trying to reference and the IndexError) but I haven't been able to find any examples of Flask using the Python CSV library to parse an uploaded file and manipulate columns in the way I need to. How can I resolve this? Any pointers in the right direction are much appreciated!

edited Nov 14 '18 at 23:01

Joel

1,5686719

asked Nov 14 '18 at 22:30

lpm

156

1

According to this question, the solution is to do request_file.read() instead of request_file.stream.read(). I've never done it that way myself but it seemed to work for that question's OP.

– noslenkwah
Nov 14 '18 at 22:44

add a comment |

Pet1,Pet2,Pet3
Cats,Dogs,Mice

And the output should look like:

Pet1,Pet2,Pet3,Pet4
Birds,Dogs,Mice,Cats

Here is my code:

from flask import Flask, make_response, request
import operator
import io
import csv

app = Flask(__name__)

def transform(text_file_contents):
 reader = csv.reader(text_file_contents)
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0))
 return sortedlist


@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 if not request_file:
 return "No file"

file_contents = request_file.stream.read().decode("utf-8")

result = transform(file_contents)

response = make_response(result)
response.headers["Content-Disposition"] = "attachment; filename=result.csv"
return response

This is the error I am getting:

Traceback (most recent call last):
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/user/mysite/callnumbers.py", line 62, in transform_view
result = transform(file_contents)
File "/home/user/mysite/callnumbers.py", line 18, in transform
row[0] = row[1]
IndexError: list index out of range

edited Nov 14 '18 at 23:01

Joel

1,5686719

asked Nov 14 '18 at 22:30

lpm

156

1

According to this question, the solution is to do request_file.read() instead of request_file.stream.read(). I've never done it that way myself but it seemed to work for that question's OP.

– noslenkwah
Nov 14 '18 at 22:44

add a comment |

Pet1,Pet2,Pet3
Cats,Dogs,Mice

And the output should look like:

Pet1,Pet2,Pet3,Pet4
Birds,Dogs,Mice,Cats

Here is my code:

from flask import Flask, make_response, request
import operator
import io
import csv

app = Flask(__name__)

def transform(text_file_contents):
 reader = csv.reader(text_file_contents)
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0))
 return sortedlist


@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 if not request_file:
 return "No file"

file_contents = request_file.stream.read().decode("utf-8")

result = transform(file_contents)

response = make_response(result)
response.headers["Content-Disposition"] = "attachment; filename=result.csv"
return response

This is the error I am getting:

Traceback (most recent call last):
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/user/mysite/callnumbers.py", line 62, in transform_view
result = transform(file_contents)
File "/home/user/mysite/callnumbers.py", line 18, in transform
row[0] = row[1]
IndexError: list index out of range

edited Nov 14 '18 at 23:01

Joel

1,5686719

asked Nov 14 '18 at 22:30

lpm

156

Pet1,Pet2,Pet3
Cats,Dogs,Mice

And the output should look like:

Pet1,Pet2,Pet3,Pet4
Birds,Dogs,Mice,Cats

Here is my code:

from flask import Flask, make_response, request
import operator
import io
import csv

app = Flask(__name__)

def transform(text_file_contents):
 reader = csv.reader(text_file_contents)
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0))
 return sortedlist


@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 if not request_file:
 return "No file"

file_contents = request_file.stream.read().decode("utf-8")

result = transform(file_contents)

response = make_response(result)
response.headers["Content-Disposition"] = "attachment; filename=result.csv"
return response

This is the error I am getting:

Traceback (most recent call last):
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
response = self.full_dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
raise value
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
rv = self.dispatch_request()
File "/home/user/.virtualenvs/myvirtualenv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/user/mysite/callnumbers.py", line 62, in transform_view
result = transform(file_contents)
File "/home/user/mysite/callnumbers.py", line 18, in transform
row[0] = row[1]
IndexError: list index out of range

python csv flask pythonanywhere

edited Nov 14 '18 at 23:01

Joel

1,5686719

asked Nov 14 '18 at 22:30

lpm

156

edited Nov 14 '18 at 23:01

Joel

1,5686719

asked Nov 14 '18 at 22:30

lpm

156

edited Nov 14 '18 at 23:01

Joel

1,5686719

edited Nov 14 '18 at 23:01

Joel

1,5686719

edited Nov 14 '18 at 23:01

Joel

1,5686719

asked Nov 14 '18 at 22:30

lpm

156

asked Nov 14 '18 at 22:30

lpm

156

asked Nov 14 '18 at 22:30

lpm

156

1

According to this question, the solution is to do request_file.read() instead of request_file.stream.read(). I've never done it that way myself but it seemed to work for that question's OP.

– noslenkwah
Nov 14 '18 at 22:44

add a comment |

1

According to this question, the solution is to do request_file.read() instead of request_file.stream.read(). I've never done it that way myself but it seemed to work for that question's OP.

– noslenkwah
Nov 14 '18 at 22:44

According to this question, the solution is to do request_file.read() instead of request_file.stream.read(). I've never done it that way myself but it seemed to work for that question's OP.

– noslenkwah
Nov 14 '18 at 22:44

add a comment |

1 Answer
1

active

oldest

votes

The csv.reader() function takes a file object instead of text. One way to do it is to save the file then reopen it in the transform function.

from flask import Flask, make_response, request
import operator
import io
import csv 

app = Flask(__name__)


def transform():
 with open('myfile.csv', 'rb') as f:
 reader = csv.reader(f) 
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0)) 
 return sortedlist

@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 request_file.save("myfile.csv")
 if not request_file:
 return "No file"
 #file_contents = io.StringIO(request_file.stream.read().decode("UTF8"), newline=None)
 #file_contents = request_file.stream.read().decode("utf-8")

 result = transform()
 print result

 response = make_response(result)
 response.headers["Content-Disposition"] = "attachment; filename=result.csv"
 return response
if __name__ == '__main__':
 app.run()

edited Nov 15 '18 at 17:03

answered Nov 15 '18 at 15:19

Mike C.

439519

add a comment |

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1 Answer
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1 Answer
1

active

oldest

votes

The csv.reader() function takes a file object instead of text. One way to do it is to save the file then reopen it in the transform function.

from flask import Flask, make_response, request
import operator
import io
import csv 

app = Flask(__name__)


def transform():
 with open('myfile.csv', 'rb') as f:
 reader = csv.reader(f) 
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0)) 
 return sortedlist

@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 request_file.save("myfile.csv")
 if not request_file:
 return "No file"
 #file_contents = io.StringIO(request_file.stream.read().decode("UTF8"), newline=None)
 #file_contents = request_file.stream.read().decode("utf-8")

 result = transform()
 print result

 response = make_response(result)
 response.headers["Content-Disposition"] = "attachment; filename=result.csv"
 return response
if __name__ == '__main__':
 app.run()

edited Nov 15 '18 at 17:03

answered Nov 15 '18 at 15:19

Mike C.

439519

add a comment |

The csv.reader() function takes a file object instead of text. One way to do it is to save the file then reopen it in the transform function.

from flask import Flask, make_response, request
import operator
import io
import csv 

app = Flask(__name__)


def transform():
 with open('myfile.csv', 'rb') as f:
 reader = csv.reader(f) 
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0)) 
 return sortedlist

@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 request_file.save("myfile.csv")
 if not request_file:
 return "No file"
 #file_contents = io.StringIO(request_file.stream.read().decode("UTF8"), newline=None)
 #file_contents = request_file.stream.read().decode("utf-8")

 result = transform()
 print result

 response = make_response(result)
 response.headers["Content-Disposition"] = "attachment; filename=result.csv"
 return response
if __name__ == '__main__':
 app.run()

edited Nov 15 '18 at 17:03

answered Nov 15 '18 at 15:19

Mike C.

439519

add a comment |

The csv.reader() function takes a file object instead of text. One way to do it is to save the file then reopen it in the transform function.

from flask import Flask, make_response, request
import operator
import io
import csv 

app = Flask(__name__)


def transform():
 with open('myfile.csv', 'rb') as f:
 reader = csv.reader(f) 
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0)) 
 return sortedlist

@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 request_file.save("myfile.csv")
 if not request_file:
 return "No file"
 #file_contents = io.StringIO(request_file.stream.read().decode("UTF8"), newline=None)
 #file_contents = request_file.stream.read().decode("utf-8")

 result = transform()
 print result

 response = make_response(result)
 response.headers["Content-Disposition"] = "attachment; filename=result.csv"
 return response
if __name__ == '__main__':
 app.run()

edited Nov 15 '18 at 17:03

answered Nov 15 '18 at 15:19

Mike C.

439519

The csv.reader() function takes a file object instead of text. One way to do it is to save the file then reopen it in the transform function.

from flask import Flask, make_response, request
import operator
import io
import csv 

app = Flask(__name__)


def transform():
 with open('myfile.csv', 'rb') as f:
 reader = csv.reader(f) 
 all = 
 row = next(reader)
 row.append('Pet4')
 all.append(row)
 for row in reader:
 pet4 = row[0]
 row[0] = "Birds"
 row.append(pet4)
 all.append(row)
 sortedlist = sorted(all, key=operator.itemgetter(0)) 
 return sortedlist

@app.route('/')
def form():
 return """
 <html>
 <body>
 <h1>Upload a CSV File</h1>

 <form action="/transform" method="post" enctype="multipart/form-data">
 <input type="file" name="data_file" />
 <input type="submit" />
 </form>
 </body>
 </html>
"""

@app.route('/transform', methods=["POST"])
def transform_view():
 request_file = request.files['data_file']
 request_file.save("myfile.csv")
 if not request_file:
 return "No file"
 #file_contents = io.StringIO(request_file.stream.read().decode("UTF8"), newline=None)
 #file_contents = request_file.stream.read().decode("utf-8")

 result = transform()
 print result

 response = make_response(result)
 response.headers["Content-Disposition"] = "attachment; filename=result.csv"
 return response
if __name__ == '__main__':
 app.run()

edited Nov 15 '18 at 17:03

answered Nov 15 '18 at 15:19

Mike C.

439519

edited Nov 15 '18 at 17:03

answered Nov 15 '18 at 15:19

Mike C.

439519

answered Nov 15 '18 at 15:19

Mike C.

439519

answered Nov 15 '18 at 15:19

Mike C.

439519

add a comment |

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