Merge pull request #14666 from ihsan314:file_io_xml_yml

Python code examples for file IO in xml and yml format

* Initial "Pythonization" of file_input_output.cpp

* Moved file_input_output.py to correct location

* Nearly done Pythonizing file_input_output.cpp

* Python equivalent of file_input_output.py created

* Started Pythonizing camera_calibration.cpp

* Completed Python tutorial/sample code for file_input_output

* Resolved whitespace issues

* Removed tabs in file_input_output.cpp

* Patched import order and wrapped code in main function

* Changed string to docstring format in help file

* Updated link to Python example code

samples/cpp/tutorial_code/core/file_input_output/file_input_output.cpp

@@ -25,6 +25,7 @@ public:
     {}
     explicit MyData(int) : A(97), X(CV_PI), id("mydata1234") // explicit to avoid implicit conversion
     {}
+    //! [inside]
     void write(FileStorage& fs) const                        //Write serialization for this class
     {
         fs << "{" << "A" << A << "X" << X << "id" << id << "}";
@@ -35,6 +36,7 @@ public:
         X = (double)node["X"];
         id = (string)node["id"];
     }
+    //! [inside]
 public:   // Data Members
     int A;
     double X;
@@ -42,6 +44,7 @@ public:   // Data Members
 };
 
 //These write and read functions must be defined for the serialization in FileStorage to work
+//! [outside]
 static void write(FileStorage& fs, const std::string&, const MyData& x)
 {
     x.write(fs);
@@ -52,6 +55,7 @@ static void read(const FileNode& node, MyData& x, const MyData& default_value =
     else
         x.read(node);
 }
+//! [outside]
 
 // This function will print our custom class to the console
 static ostream& operator<<(ostream& out, const MyData& m)
@@ -72,27 +76,48 @@ int main(int ac, char** av)
 
     string filename = av[1];
     { //write
+        //! [iomati]
         Mat R = Mat_<uchar>::eye(3, 3),
             T = Mat_<double>::zeros(3, 1);
+        //! [iomati]
+        //! [customIOi]
         MyData m(1);
+        //! [customIOi]
 
+        //! [open]
         FileStorage fs(filename, FileStorage::WRITE);
+        // or:
+        // FileStorage fs;
+        // fs.open(filename, FileStorage::WRITE);
+        //! [open]
 
+        //! [writeNum]
         fs << "iterationNr" << 100;
+        //! [writeNum]
+        //! [writeStr]
         fs << "strings" << "[";                              // text - string sequence
         fs << "image1.jpg" << "Awesomeness" << "../data/baboon.jpg";
         fs << "]";                                           // close sequence
+        //! [writeStr]
 
+        //! [writeMap]
         fs << "Mapping";                              // text - mapping
         fs << "{" << "One" << 1;
         fs <<        "Two" << 2 << "}";
+        //! [writeMap]
 
+        //! [iomatw]
         fs << "R" << R;                                      // cv::Mat
         fs << "T" << T;
+        //! [iomatw]
 
+        //! [customIOw]
         fs << "MyData" << m;                                // your own data structures
+        //! [customIOw]
 
+        //! [close]
         fs.release();                                       // explicit close
+        //! [close]
         cout << "Write Done." << endl;
     }
 
@@ -101,9 +126,11 @@ int main(int ac, char** av)
         FileStorage fs;
         fs.open(filename, FileStorage::READ);
 
+        //! [readNum]
         int itNr;
         //fs["iterationNr"] >> itNr;
         itNr = (int) fs["iterationNr"];
+        //! [readNum]
         cout << itNr;
         if (!fs.isOpened())
         {
@@ -112,6 +139,7 @@ int main(int ac, char** av)
             return 1;
         }
 
+        //! [readStr]
         FileNode n = fs["strings"];                         // Read string sequence - Get node
         if (n.type() != FileNode::SEQ)
         {
@@ -122,19 +150,26 @@ int main(int ac, char** av)
         FileNodeIterator it = n.begin(), it_end = n.end(); // Go through the node
         for (; it != it_end; ++it)
             cout << (string)*it << endl;
+        //! [readStr]
 
 
+        //! [readMap]
         n = fs["Mapping"];                                // Read mappings from a sequence
         cout << "Two  " << (int)(n["Two"]) << "; ";
         cout << "One  " << (int)(n["One"]) << endl << endl;
+        //! [readMap]
 
 
         MyData m;
         Mat R, T;
 
+        //! [iomat]
         fs["R"] >> R;                                      // Read cv::Mat
         fs["T"] >> T;
+        //! [iomat]
+        //! [customIO]
         fs["MyData"] >> m;                                 // Read your own structure_
+        //! [customIO]
 
         cout << endl
             << "R = " << R << endl;
@@ -142,9 +177,11 @@ int main(int ac, char** av)
         cout << "MyData = " << endl << m << endl << endl;
 
         //Show default behavior for non existing nodes
+        //! [nonexist]
         cout << "Attempt to read NonExisting (should initialize the data structure with its default).";
         fs["NonExisting"] >> m;
         cout << endl << "NonExisting = " << endl << m << endl;
+        //! [nonexist]
     }
 
     cout << endl

samples/python/tutorial_code/core/file_input_output/file_input_output.py

+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+import sys
+
+def help(filename):
+    print (
+        '''
+        {0} shows the usage of the OpenCV serialization functionality. \n\n
+        usage:\n
+            python3 {0} outputfile.yml.gz\n\n
+        The output file may be either in XML, YAML or JSON. You can even compress it\n
+        by specifying this in its extension like xml.gz yaml.gz etc... With\n
+        FileStorage you can serialize objects in OpenCV.\n\n
+        For example: - create a class and have it serialized\n
+                     - use it to read and write matrices.\n
+        '''.format(filename)
+    )
+
+class MyData:
+    A = 97
+    X = np.pi
+    name = 'mydata1234'
+
+    def __repr__(self):
+        s = '{ name = ' + self.name + ', X = ' + str(self.X)
+        s = s + ', A = ' +  str(self.A) + '}'
+        return s
+
+    ## [inside]
+    def write(self, fs):
+        fs.write('MyData','{')
+        fs.write('A', self.A)
+        fs.write('X', self.X)
+        fs.write('name', self.name)
+        fs.write('MyData','}')
+
+    def read(self, node):
+        if (not node.empty()):
+            self.A = int(node.getNode('A').real())
+            self.X = node.getNode('X').real()
+            self.name = node.getNode('name').string()
+        else:
+            self.A = self.X = 0
+            self.name = ''
+    ## [inside]
+
+def main(argv):
+    if len(argv) != 2:
+        help(argv[0])
+        exit(1)
+
+    # write
+    ## [iomati]
+    R = np.eye(3,3)
+    T = np.zeros((3,1))
+    ## [iomati]
+    ## [customIOi]
+    m = MyData()
+    ## [customIOi]
+
+    filename = argv[1]
+
+    ## [open]
+    s = cv.FileStorage(filename, cv.FileStorage_WRITE)
+    # or:
+    # s = cv.FileStorage()
+    # s.open(filename, cv.FileStorage_WRITE)
+    ## [open]
+
+    ## [writeNum]
+    s.write('iterationNr', 100)
+    ## [writeNum]
+
+    ## [writeStr]
+    s.write('strings', '[')
+    s.write('image1.jpg','Awesomeness')
+    s.write('../data/baboon.jpg',']')
+    ## [writeStr]
+
+    ## [writeMap]
+    s.write ('Mapping', '{')
+    s.write ('One', 1)
+    s.write ('Two', 2)
+    s.write ('Mapping', '}')
+    ## [writeMap]
+
+    ## [iomatw]
+    s.write ('R_MAT', R)
+    s.write ('T_MAT', T)
+    ## [iomatw]
+
+    ## [customIOw]
+    m.write(s)
+    ## [customIOw]
+    ## [close]
+    s.release()
+    ## [close]
+    print ('Write Done.')
+
+    # read
+    print ('\nReading: ')
+    s = cv.FileStorage()
+    s.open(filename, cv.FileStorage_READ)
+
+    ## [readNum]
+    n = s.getNode('iterationNr')
+    itNr = int(n.real())
+    ## [readNum]
+    print (itNr)
+
+    if (not s.isOpened()):
+        print ('Failed to open ', filename, file=sys.stderr)
+        help(argv[0])
+        exit(1)
+
+    ## [readStr]
+    n = s.getNode('strings')
+    if (not n.isSeq()):
+        print ('strings is not a sequence! FAIL', file=sys.stderr)
+        exit(1)
+
+    for i in range(n.size()):
+        print (n.at(i).string())
+    ## [readStr]
+
+    ## [readMap]
+    n = s.getNode('Mapping')
+    print ('Two',int(n.getNode('Two').real()),'; ')
+    print ('One',int(n.getNode('One').real()),'\n')
+    ## [readMap]
+
+    ## [iomat]
+    R = s.getNode('R_MAT').mat()
+    T = s.getNode('T_MAT').mat()
+    ## [iomat]
+    ## [customIO]
+    m.read(s.getNode('MyData'))
+    ## [customIO]
+
+    print ('\nR =',R)
+    print ('T =',T,'\n')
+    print ('MyData =','\n',m,'\n')
+
+    ## [nonexist]
+    print ('Attempt to read NonExisting (should initialize the data structure',
+            'with its default).')
+    m.read(s.getNode('NonExisting'))
+    print ('\nNonExisting =','\n',m)
+    ## [nonexist]
+
+    print ('\nTip: Open up',filename,'with a text editor to see the serialized data.')
+
+if __name__ == '__main__':
+    main(sys.argv)