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

@@ -0,0 +1,156 @@
+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)