Saving uploaded files in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save an uploaded file in Flask.

Flask

file = request.files['file']
file.[1]('uploads/' + file.filename)

Drag options to blanks, or click blank then click option'

Aupload

Bopen

Cwrite

Dsave

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'write' instead of 'save' causes an error because 'write' is not a method of the file object.

Using 'open' is incorrect because it is a built-in function, not a method of the uploaded file.

The save method stores the uploaded file to the given path.

2fill in blank

medium

Complete the code to check if the uploaded file has a filename before saving.

Flask

if file.[1] != '':
    file.save('uploads/' + file.filename)

Drag options to blanks, or click blank then click option'

Apath

Bfilename

Cfile

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' instead of 'filename' will cause an AttributeError.

Checking 'file' or 'path' attributes does not give the filename.

The filename attribute holds the name of the uploaded file.

3fill in blank

hard

Fix the error in the code to securely save the uploaded file using Werkzeug's secure_filename.

Flask

from werkzeug.utils import [1]
filename = secure_filename(file.filename)
file.save('uploads/' + filename)

Drag options to blanks, or click blank then click option'

Asecure_filename

Bfilename_secure

Csafe_filename

Dsecure_file

Attempts:

3 left

💡 Hint

Common Mistakes

Importing a non-existent function like 'secure_file' causes ImportError.

Using wrong function names leads to NameError.

The correct import is secure_filename from werkzeug.utils.

4fill in blank

hard

Fill both blanks to save the uploaded file securely in a folder named 'uploads'.

Flask

from werkzeug.utils import [1]
filename = [2](file.filename)
file.save('uploads/' + filename)

Drag options to blanks, or click blank then click option'

Asecure_filename

Bsafe_name

Csanitize_filename

Dclean_filename

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for import and usage causes NameError.

Using made-up function names causes ImportError.

Both blanks require secure_filename to import and use the function correctly.

5fill in blank

hard

Fill all three blanks to check if a file was uploaded, secure its filename, and save it.

Flask

if '[1]' in request.files:
    file = request.files['file']
    if file.[2] != '':
        from werkzeug.utils import [3]
        filename = secure_filename(file.filename)
        file.save('uploads/' + filename)

Drag options to blanks, or click blank then click option'

Afile

Bfilename

Csecure_filename

Dupload

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong keys in request.files causes KeyError.

Not checking if filename is empty can cause saving errors.

Importing wrong function names causes ImportError.

The code checks if 'file' is in the uploaded files, then checks filename attribute, imports secure_filename, and saves the file securely.

Practice

1. In Flask, which object do you use to access files uploaded by a user in a form?

easy

A. request.args

B. request.files

C. request.data

D. request.form

Solution

1. Step 1: Understand Flask request objects

   Flask provides different objects to access data sent by the client. request.files holds uploaded files.

2. Step 2: Identify correct object for files

   request.form is for form fields, request.data is raw data, and request.args is for URL query parameters.

3. Final Answer:

   request.files -> Option B

4. Quick Check:

   Uploaded files = request.files [OK]

Hint: Uploaded files are always in request.files [OK]

Common Mistakes:

• Using request.form to get files
• Trying to access files from request.args
• Confusing request.data with files

2. Which of the following is the correct way to save an uploaded file named file to a folder called uploads in Flask?

easy

A. file.save('uploads/' + file.filename)

B. file.save(file.filename)

C. save(file, 'uploads/')

D. request.save(file, 'uploads/')

Solution

1. Step 1: Use the file object's save method

   The uploaded file object has a save() method that takes the full path to save the file.

2. Step 2: Provide correct path including folder and filename

   Concatenate the folder path and the file's filename to save it in the right place.

3. Final Answer:

   file.save('uploads/' + file.filename) -> Option A

4. Quick Check:

   Use file.save(path) with full path [OK]

Hint: Use file.save('folder/' + file.filename) to save files [OK]

Common Mistakes:

• Calling save() without a path
• Using save() as a standalone function
• Not including folder path in save()

3. What will happen when this Flask code runs after a file upload?

file = request.files['photo']
file.save('/tmp/' + file.filename)
return 'Saved!'

medium

A. Nothing is saved because request.files['photo'] is empty by default

B. The file is saved but the filename is lost, causing an error

C. The code raises an error because save() needs a full absolute path

D. The uploaded file is saved in /tmp/ with its original filename and 'Saved!' is returned

Solution

1. Step 1: Access the uploaded file from request.files

   The code gets the file named 'photo' from the uploaded files correctly.

2. Step 2: Save the file to /tmp/ folder with original filename

   Calling save() with '/tmp/' + filename saves the file in that folder.

3. Final Answer:

   The uploaded file is saved in /tmp/ with its original filename and 'Saved!' is returned -> Option D

4. Quick Check:

   save() stores file at given path, returns confirmation [OK]

Hint: save() stores file at given path, returns confirmation [OK]

Common Mistakes:

• Assuming save() needs absolute path always
• Thinking request.files['photo'] is empty without upload
• Confusing save() behavior with form data saving

4. Identify the error in this Flask code snippet for saving an uploaded file:

file = request.files['file']
file.save(file.filename)

medium

A. Missing folder path in save() can cause files to save in wrong location

B. Using request.files instead of request.form causes error

C. file.save() requires a file object, not a filename string

D. file.filename is not a valid attribute of the file object

Solution

1. Step 1: Check the save() method argument

   The code saves the file using only the filename, without specifying a folder path.

2. Step 2: Understand file saving location

   Without a folder path, the file saves in the current working directory, which may be unintended or insecure.

3. Final Answer:

   Missing folder path in save() can cause files to save in wrong location -> Option A

4. Quick Check:

   Always include folder path in save() [OK]

Hint: Always include folder path in save() to control file location [OK]

Common Mistakes:

• Not specifying folder path in save()
• Confusing request.files with request.form
• Assuming file.filename is invalid

5. You want to securely save an uploaded file in Flask to the uploads folder, avoiding unsafe filenames. Which code snippet correctly achieves this?

from werkzeug.utils import secure_filename
file = request.files['file']
filename = secure_filename(file.filename)
file.save(f'uploads/{filename}')

hard

A. The code will fail because secure_filename() returns a file object, not a string

B. secure_filename() is unnecessary; file.save() cleans filenames automatically

C. This code safely saves the file with a cleaned filename in uploads folder

D. You must manually create the uploads folder before saving, or it errors

Solution

1. Step 1: Use secure_filename to clean the filename

   The function secure_filename() removes unsafe characters to prevent security issues.

2. Step 2: Save the file with the cleaned filename in the uploads folder

   Using file.save() with the cleaned filename inside the uploads folder saves the file securely.

3. Final Answer:

   This code safely saves the file with a cleaned filename in uploads folder -> Option C

4. Quick Check:

   Use secure_filename() before saving uploaded files [OK]

Hint: Use secure_filename() to avoid unsafe file names [OK]

Common Mistakes:

• Skipping secure_filename and risking unsafe filenames
• Assuming save() cleans filenames automatically
• Not creating uploads folder before saving