"No such file or directory" error when using "cat" in python

Question

When I use

cat folder1/folder2/*_in.txt>>output.txt 

directly in the terminal, it works fine.

But when I call from inside the python process, it shows an error "No such file or directory" :

command = "cat "+path+"*_in.txt >> " + output_variable
print(command) # print exactly the same.
os.system(command) # error : cat: folder1/folder2/*_in.txt: No such file or directory

Answer 1

This happens when there are no files matching the pattern:

$ python -c 'import os; os.system("cat *.txt")'
cat: '*.txt': No such file or directory

$ echo 'Hello World' > myfile.txt

$ python -c 'import os; os.system("cat *.txt")'
Hello World

Be aware that files are matched relative to the process's current working directory ( os.getcwd() ), and not relative to the Python file. If you can't figure out the working directory and correct relative path to your files, use absolute paths.