类型错误：返回类型必须是字符串、字典、元组、响应实例或可调用的 WSGI，但它是一个列表

Question

I'm making a Flask App that would take an image input,process it and save the results in a JSON file,but after processing the image it gives me a Type Error mentioned in the title.To add more,it prints only one line and then stops; Below is my Flask API that I'm using;

    @app.route('/upload',methods=['GET','POST'])
def upload_analyze():

    if request.method == 'POST':
        # check if a file was passed into the POST request
        if 'file' not in request.files:
            flash('No file was uploaded.')
            return redirect(request.url)     
        f = request.files['file']
        filename = secure_filename(f.filename)
        f.save(filename)
        image = cv2.imread(filename)
        #f.save(secure_filename(f.filename))    

        #return 'file uploaded successfully'
        # image_file = request.files['image']


        clt = KMeans(n_clusters = 3)
        dataset = pd.read_csv('bb22.csv') 
        X = dataset.iloc[:, 1: 8].values
        sc = StandardScaler()
        global orig , r
            # load the image, convert it to grayscale, and blur it slightly
        #images = np.array(Image.open(image_file))
        gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
        gray = cv2.GaussianBlur(gray, (7, 7), 0)

            # perform edge detection, then perform a dilation + erosion to
            # close gaps in between object edges
        edged = cv2.Canny(gray, 50, 100)
        edged = cv2.dilate(edged, None, iterations=1)
        edged = cv2.erode(edged, None, iterations=1)

            # find contours in the edge map
        cnts = cv2.findContours(edged.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
        cnts = cnts[0] if imutils.is_cv2() else cnts[1]

            # sort the contours from left-to-right and initialize the
            # 'pixels per metric' calibration variable
        (cnts, _) = contours.sort_contours(cnts)
        pixelsPerMetric = None

        object_num = 0
        r=object_num
        objects = []

        idx=0

        orig = image.copy()
        counter = 0
        leng = [0] * 400
        width = [0] *400
            # loop over the contours individually
        for c in cnts:
# if the contour is not sufficiently large, ignore it
            if cv2.contourArea(c) < 50:
                continue
                # compute the rotated bounding box of the contour
            box = cv2.minAreaRect(c)
            box = cv2.cv.BoxPoints(box) if imutils.is_cv2() else cv2.boxPoints(box)
            box = np.array(box, dtype="int")
                # order the points in the contour such that they appear
                # in top-left, top-right, bottom-right, and bottom-left
                 # order, then draw the outline of the rotated bounding box
            box = perspective.order_points(box)
            cv2.drawContours(orig, [box.astype("int")], -1, (0, 255, 0), 2)
            box.astype
                 # unpack the ordered bounding box, then compute the midpoint
                 # between the top-left and top-right coordinates, followed by
                 # the midpoint between bottom-left and bottom-right coordinates
            (tl, tr, br, bl) = box
            (tltrX, tltrY) = midpoint(tl, tr)
            (blbrX, blbrY) = midpoint(bl, br)
                 # compute the midpoint between the top-left and top-right points,
                 # followed by the midpoint between the top-righ and bottom-right
            (tlblX, tlblY) = midpoint(tl, bl)
            (trbrX, trbrY) = midpoint(tr, br)

                 # compute the Euclidean distance between the midpoints
            dA = dist.euclidean((tltrX, tltrY), (blbrX, blbrY))
            dB = dist.euclidean((tlblX, tlblY), (trbrX, trbrY))

                 # if the pixels per metric has not been initialized, then
                 # compute it as the ratio of pixels to supplied metric (in this case, inches)
            if pixelsPerMetric is None:
                pixelsPerMetric = dB / 22.599 #previously its /22.50

                 # compute the size of the object
            area = round(cv2.contourArea(c) / (pixelsPerMetric**2), 3)
            perimeter = round(cv2.arcLength(c, True)/ pixelsPerMetric, 3)
            hull = cv2.convexHull(c)
            hull_area = round(cv2.contourArea(hull) / (pixelsPerMetric**2), 3)
            (x,y),(ma,MA),angle = cv2.fitEllipse(c)
            eccentricity = round(np.sqrt(1-(ma/MA)**2),3)
            C = round(4*np.pi*area/perimeter**2, 3)
            dimA = round(dA / pixelsPerMetric, 3)
            dimB = round(dB / pixelsPerMetric, 3)
            if (dimA >= dimB):
                temp=dimA
                dimA=dimB
                dimB=temp

            leng[counter] = str(dimB)
            width[counter] = str(dimA)
            counter = counter +1

            x,y,w,h = cv2.boundingRect(c)
            idx+=1
            mask = np.zeros(image.shape[:2],np.uint8)
            cv2.drawContours(mask, [c],-1, 255, -1)
            dst = cv2.bitwise_and(image, image, mask=mask)
            new_img=dst[y-20:y+h+20,x-20:x+w+20]

                # pre-process the image for classification
            if len(new_img) == 0:
                WB = 0
                continue

            object_num = object_num+1
            image1 = cv2.cvtColor(new_img, cv2.COLOR_BGR2RGB)
            image1 = new_img.reshape((image1.shape[0] * new_img.shape[1], 3))

                #classify color
            clt.fit(image1)
            count = 0
            global dominant_color
            dominant_color = [0,0,0]

            for (color) in (clt.cluster_centers_):
                a = [color.astype("uint8").tolist()[0], color.astype("uint8").tolist()[1],
                 color.astype("uint8").tolist()[2]]
                count = count+1
                if(count == 2) and (a != [0, 0, 0]):
                    dominant_color = a

                #prepare image for broken classification
            new_img = cv2.resize(new_img, (64, 64))
            new_img = new_img.astype("float") / 255.0
            new_img = img_to_array(new_img)
            new_img = np.expand_dims(new_img, axis=0)

                # classify the input image
            with graph.as_default():

                (yes, no) = model.predict(new_img)[0]

                    # build the label
                if (yes > no):
                    WB = 0
                    y_new = "Broken"
                else:

                    if object_num == 1:
                        print("true")
                        continue
                    WB = 1
                    X_new = array([[dimA, dimB, area, perimeter, hull_area, eccentricity, C]])
                    X=sc.fit_transform(X)
                    X_new = sc.transform(X_new)
                    y_new = type_model.predict(X_new)
                    print("X=%s, Predicted=%s" % (X_new[0], y_new))

                    obj_num=object_num-1 # because one item on the left most side we have for the pixel constant value


                content = {
                    "Object_number": obj_num,
                    "Width": dimA,
                    "Length": dimB,
                    #"Area": area,
                    #"Perimeter": perimeter,
                    #"hull_area": hull_area,
                    #"eccentricity": eccentricity,
                    #"compactness": C,
                    "WB": WB # Whole or Broken
                    #"Type": str(y_new[0]),
                    #"color_rgb": dominant_color,
                    #"color_hex": rgb2hex(dominant_color[2], dominant_color[1], dominant_color[0])
                    }

                objects.append(content)

            return(objects)

        objects=analyze()
        with open('test6.json', 'w') as fout:
            json.dump(objects , fout)
        print(objects)
        print(type(objects))
        return 'ok'

Also in console only this 1 line gets printed:

X=[ 0.38739663 -0.25583995  0.22674784 -0.2933872   0.19980647 -0.03758974
  0.4759277 ], Predicted=[4]

I'm returning this message to make sure that the JSON file is created but it doesn't gets created..I can't figure out what is wrong with the return type..kindly help.

Answer 1

The views in Flask require a hashable return type. You can always convert your return values to hashable types viz string, dict, tuple etc and then transform from the result.

return { "data": [ { "name": "my name", age: "27" } ] }

Answer 2

User oz19 commented

You need to serialize objects before returning. import json and then json.dumps(objects)

and also

You have a return(objects) at the end of for c in cnts . That could be the problem

So the solution if, not using jsonify , is to call json.dumps on the list before returning it.

Answer 3

If you are using this below method, you can easily get required data in json format

# don't forgot to import jsonify

from flask import Flask, request, redirect, jsonify
@app.route('/sample', methods = ['GET', 'POST'])
def sample():
    if(request.method == 'GET'): # i am using get you can change whatever you want
        data = [{"A": "a",
                 "B": "b",
                 "C": "c",
               }]
        return jsonify({'data': data})
# now you can start your json dumping process here after

Hope it helps!