If the reason you're checking is so you can do something like if file_exists: open_it()
, it's safer to use a try
around the attempt to open it. Checking and then opening risks the file being deleted or moved or something between when you check and when you try to open it.
If you're not planning to open the file immediately, you can use os.path.isfile
Return True
if path is an existing regular file. This follows symbolic links, so both islink() and isfile() can be true for the same path.
import os.path
os.path.isfile(fname)
if you need to be sure it's a file.
Starting with Python 3.4, the pathlib
module offers an object-oriented approach (backported to pathlib2
in Python 2.7):
from pathlib import Path
my_file = Path("/path/to/file")
if my_file.is_file():
# file exists
To check a directory, do:
if my_file.is_dir():
# directory exists
To check whether a Path
object exists independently of whether is it a file or directory, use exists()
:
if my_file.exists():
# path exists
You can also use resolve(strict=True)
in a try
block:
try:
my_abs_path = my_file.resolve(strict=True)
except FileNotFoundError:
# doesn't exist
else:
# exists
You create a new key/value pair on a dictionary by assigning a value to that key
d = {'key': 'value'}
print(d) # {'key': 'value'}
d['mynewkey'] = 'mynewvalue'
print(d) # {'key': 'value', 'mynewkey': 'mynewvalue'}
If the key doesn't exist, it's added and points to that value. If it exists, the current value it points to is overwritten.
Best Answer
You can specify a python write mode in the pandas
to_csv
function. For append it is 'a'.In your case:
The default mode is 'w'.