如何打开文件并将其写入现有目录

Question

We are new to python and trying to write to a new file in an existing directory cyt_dir

outfile = open('cyt_dir/' +s+ ".html", "w")

but we are getting

IOerror [ERRno2] No such file or directory: 'cyt_dir/

why doesn't it recognise the directory?

Answer 1

The code you have written works no problem.

>>> s = "face"
>>> f = open('cyt_dir/' +s+ ".html", "w")
>>> f.write("testy testerson")
>>> f.close()

This succesfully writes to the correct directory. The error you got is an IOerror and so suggests something else is at play here.

Looking at the IOerror documentation on python.org we can see some reasons as to why this might pop up. No such file or directory suggests a few different things to me.

1. You're running the python file from a directory where this folder structure doesn't exist.
2. You're running the python file as a user that perhaps doesn't have permissions to that directory. (I suspect a different Errno would demonstrate that)
3. Your harddrive is full or something daft like that.

All in all this is just speculation. You might be able to get more info from the error if you catch it:

try:
    f = open('cyt_dir/' +s+ ".html", "w")
except IOError, e:
    print "Not allowed", e

Answer 2

Most likely this is current path issue, you need to know where you are executing your script from. Or, as an alternative, provide an absolute path instead of relative cyt_dir .

I would pick third variant and would write a mechanism that extracts the path from script location, so that you are always safe, not matter what:

path = os.path.dirname(os.path.abspath(__file__))
try:
    outfile = open("%s/cyt_dir/%s.html".format(path, s), "w")
except IOError as e:
    print "I/O error({0}): {1}".format(e.errno, e.strerror)