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I expected the variable output_format to be a string. But when I ran the script it gave me a tuple type and threw an exception.
If I run in Python interpreter, it gave me an expected string.
('--sout "#standard{access=file,vcodec=h264,dst=c0_s0_h264_640x480_30_vbr_500_99_40000000.mp4}"',)
'h264'
<type 'str'>
Traceback (most recent call last):
File "streaming_verification/src/streaming_verification/scripts/streaming_verification.py", line 184, in run
self.streaming.dump_file(export_fname, 5, codec_type)
File "streaming_verification/src/streaming_verification/scripts/streaming.py", line 57, in dump_file
cmd_str = " ".join(cmd)
TypeError: sequence item 3: expected string, tuple found
Script source code:
def dump_file(self,
fname='',
period=10,
codec_type="h264"):
if "h264" == codec_type:
output_format = "--sout \"#standard{access=file,vcodec=h264,dst=%s.mp4}\"" % fname,
elif "mjpeg" == codec_type:
output_format = "--sout \"#standard{access=file,vcodec=mjpg ,dst=%s.avi}\"" % fname,
elif "mpeg" == codec_type :
output_format = "--sout \"#standard{access=file,vcodec=h264,dst=%s.mp4}\"" % fname,
pp(output_format)
cmd =[
"vlc",
"-I dummy",
"--rtsp-tcp {0}".format(self.conn_cfg["rtsp_link"]),
output_format,
"--stop-time {0} vlc://quit ".format(period)
]
cmd_str = " ".join(cmd)
self.run(cmd_str)
565
Tuple they are immutable like strings and sequence like lists. They are used to store data just like list, just like string you cannot update or edit the tuple to change it you have to create a new one just like strings. Tuples can be created using parenthesis () and data is inserted using comas.
Method #1 : Using * operator The multiplication operator can be used to construct the duplicates of a container. This also can be extended to tuples even though tuples are immutable.
Tuples can be a collection of various data types, and unlike simpler data types, conventional methods of getting the type of each element of tuple is not possible.
Using the '*' operator. The repetition operator duplicates a tuple and links all of them together. Even though tuples are immutable, this can be extended to them.
Your output_format is always tuple, because you put a comma after each possible value:
output_format = "..." % fname,
# ---------------------------^
Remove those commas and your cmd_str will once again only contain strings.
Python tuples are formed by such commas; the parenthesis are only needed when not using them would lead to ambiguity:
>>> 1
1
>>> 1,
(1,)
>>> type(_)
<class 'tuple'>
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