I have a script which wants to load integers from a text file. If the file does not exist I want the user to be able to browse for a different file (or the same file in a different location, I have UI implementation for that).
What I don't get is what the purpose of Exception handling, or catching exceptions is. From what I have read it seems to be something you can use to log errors, but if an input is needed catching the exception won't fix that. I am wondering if a while loop in the except block is the approach to use (or don't use the try/except for loading a file)?
with open(myfile, 'r') as f:
try:
with open(myfile, 'r') as f:
contents = f.read()
print("From text file : ", contents)
except FileNotFoundError as Ex:
print(Ex)
You need to use to while loop and use a variable to verify in the file is found or not, if not found, set in the input the name of the file and read again and so on:
filenotfound = True
file_path = myfile
while filenotfound:
try:
with open(file_path, 'r') as f:
contents = f.read()
print("From text file : ", contents)
filenotfound = False
except FileNotFoundError as Ex:
file_path = str(input())
filenotfound = True
Related
recently i started learning Python and encountered a problem i can`t find an answer to.
Idea of the program is to ask for username, load a dictionary from JSON file, and if the name is in the dictionary - print the users favourite number.
The code, that loads the JSON file looks like this:
import json
fav_numbers = {}
filename = 'numbers.JSON'
name = input('Hi, what`s your name? ')
try:
with open(filename) as f_obj:
fav_numbers = json.load(f_obj)
except FileNotFoundError:
pass
if name in fav_numbers.keys():
print('Hi {}, your fav number is {}, right?'.format(name, fav_numbers[name]))
else:
number = input('Hi {}, what`s your favourte number? '.format(name))
fav_numbers[name] = number
with open(filename, 'w') as f_obj:
json.dump(fav_numbers, filename)
Still, as i try to run it, it crashes, telling me:
Exception has occurred: FileNotFoundError
[Errno 2] No such file or directory: 'numbers.JSON'
File "/home/niedzwiedx/Dokumenty/Python/ulubionejson.py", line 22, in <module>
with open(filename) as f_obj:
What i`m doing wrong to catch the exception? (Already tried changing the FileNotFoundError to OSError or IOError)
The error comes from you last line, outside of your try/except
with open(filename, 'w') as f_obj:
json.dump(fav_numbers, filename)
filename is a string, not a file.
You have to use
with open(filename, 'w') as f_obj:
json.dump(fav_numbers, f_obj)
For additional safety, you can surround this part with try/except too
try:
with open(filename, 'w') as f_obj:
json.dump(fav_numbers, f_obj)
except (FileNotFoundError, PremissionError):
print("Impossible to create JSON file to save data")
I am writing a program which stores some JSON-encoded data in a file, but sometimes the resulting file is blank (because there wasn't found any new data). When the program finds data and stores it, I do this:
with open('data.tmp') as f:
data = json.load(f)
os.remove('data.tmp')
Of course, if the file is blank this will raise an exception, which I can catch but does not let me to remove the file. I have tried:
try:
with open('data.tmp') as f:
data = json.load(f)
except:
os.remove('data.tmp')
And I get this error:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "MyScript.py", line 50, in run
os.remove('data.tmp')
PermissionError: [WinError 32] The process cannot access the file because it is being used by another process
How could I delete the file when the exception occurs?
How about separating out file reading and json loading? json.loads behaves exactly same as json.load but uses a string.
with open('data.tmp') as f:
dataread = f.read()
os.remove('data.tmp')
#handle exceptions as needed here...
data = json.loads(dataread)
I am late to the party. But the json dump and load modules seem to keep using files even after writing or reading data from them. What you can do is use dumps or loads modules to get the string representation and then use normal file.write() or file.read() on the result.
For example:
with open('file_path.json'), 'w') as file:
file.write(json.dumps(json_data))
os.remove('file_path.json')
Not the best alternative but it saves me a lot especially when using temp dir.
you need to edit the remove part, so it handles the non-existing case gracefully.
import os
try:
fn = 'data.tmp'
with open(fn) as f:
data = json.load(f)
except:
try:
if os.stat(fn).st_size > 0:
os.remove(fn) if os.path.exists(fn) else None
except OSError as e: # this would be "except OSError, e:" before Python 2.6
if e.errno != errno.ENOENT:
raise
see also Most pythonic way to delete a file which may not exist
you could extract the silent removal in a separate function.
also, from the same other SO question:
# python3.4 and above
import contextlib, os
try:
fn = 'data.tmp'
with open(fn) as f:
data = json.load(f)
except:
with contextlib.suppress(FileNotFoundError):
if os.stat(fn).st_size > 0:
os.remove(fn)
I personally like the latter approach better - it's explicit.
try:
masterpath = os.path.join(path, "master.txt")
with open(masterpath, 'r') as f:
s = f.read()
f.close()
exec(s)
with open(masterpath, 'w') as g:
g.truncate()
g.close()
os.remove(masterpath)
Here I want to read something in a .txt file and then erase content and delete it. But it always shows it cannot delete it as 'The process cannot access the file because it is being used by another process'.
Actually what I need is to delete the .txt file, but it cannot delete immediately sometimes, so I erase the content at first in case that it will be read again. So is there any good way to read something in a .txt file and then delete this file as soon and stable as possible?
You should NOT call f.close() nor g.close(). It is called automatically by with statement.
remove the unnecessary close() statements to start - like #grapes mentioned - why are you truncating what you are deleting? just delete it...
try:
masterpath = os.path.join(path, "master.txt")
with open(masterpath, 'r') as f:
s = f.read()
exec(s)
except Error as e:
print(e)
else:
os.remove(masterpath)
FYI, it is bad form to execute the contents of a file if you do not control the contents of said file.
another option:
masterpath = os.path.join(path, "master.txt")
with open(masterpath, 'r') as f:
try:
s = f.read()
except Error as e:
print(e)
else:
exec(s)
os.remove(masterpath)
Try to use short sleep in exception part:
try:
masterpath = os.path.join(path, "master.txt")
with open(masterpath, 'r') as f:
s = f.read()
f.close()
exec(s)
with open(masterpath, 'w') as g:
g.truncate()
g.close()
os.remove(masterpath)
except WindowsError:
time.sleep(sleep)
else:
break
Another way is to use:
os.remove(masterpath)
My code snippet can extract file from GZ as save it as .txt file, but sometimes that file may contain some weird text which crashes extract module.
Some Gibberish from file:
Method I use:
def unpackgz(name ,path):
file = path + '\\' +name
outfilename = file[:-3]+".txt"
inF = gzip.open(file, 'rb')
outF = open(outfilename, 'wb')
outF.write( inF.read() )
inF.close()
outF.close()
My question how I can go around this? Something maybe similar to with open(file, errors='ignore') as fil: . Because With that method I can extract only healthy files.
EDIT to First question
def read_corrupted_file(filename):
with gzip.open(filename, 'r') as f:
for line in f:
try:
string+=line
except Exception as e:
print(e)
return string
newfile = open("corrupted.txt", 'a+')
cwd = os.getcwd()
srtNameb="service"+str(46)+"b.gz"
localfilename3 = cwd +'\\'+srtNameb
newfile.write(read_corrupted_file(localfilename3))
Results in multiple errors:
Like This
Fixed to working state:
def read_corrupted_file(filename):
string=''
newfile = open("corrupted.txt", 'a+')
try:
with gzip.open(filename, 'rb') as f:
for line in f:
try:
newfile.write(line.decode('ascii'))
except Exception as e:
print(e)
except Exception as e:
print(e)
cwd = os.getcwd()
srtNameb="service"+str(46)+"b.gz"
localfilename3 = cwd +'\\'+srtNameb
read_corrupted_file(localfilename3)
print('done')
Generally if the file is corrupt then it will throw a error trying to unzip the file, there is not much you can do simply to still get the data, but if you just want to stop it crashing you could use a try catch.
try:
pass
except Exception as error:
print(error)
Applying this logic you could read line by line with gzip, with a try exception, after, still reading the next line when it hits a corrupted section.
import gzip
with gzip.open('input.gz','r') as f:
for line in f:
print('got line', line)
I have a directory that has bunch of sub directories, each subdir has many csv files, but I am only interest in certain csv file. So I wrote following python method, but I am unable to capture the file name, if I do *.csv it will find all the file but I don't want to all the files to be read in:
def gatherStats(template_file, csv_file):
for lang in getLanguageCodes(csv_file):
lang_dir = os.path.join(template_file, lang)
try:
for file in os.listdir(lang_dir):
if fnmatch.fnmatch(file, '*-*-template-users-data.csv'):
t_file = open(file, 'rb').read()
reader = csv.reader()
for row in reader:
print row
else:
print "didn't find the file"
except Exception, e:
logging.exception(e)
What am I doing wrong here? Is it a regular expression issue? Can we use regular expression with fnmath?
There are several problems with your code. Fix them first, then we might get to the bottom of what your issue really is.
First of all, don't use built-in names as variables, such as file. Rather replace it with filename.
Then os.path.join(lang_dir, filename) before opening the file. Meaning:
t_file = open(os.path.join(lang_dir, filename), 'rb').read()
How do you expect reader = csv.reader() to read your file if you don't reference your open file object in this line?
Your try/except block is a bit too wide for my taste. Take your time and narrow down the errors that actually can happen. Then decide which of them you want to ignore and which should crash your program. Take a close look at the exceptions actually thrown in this block. You'll probably find your issue there.
With the help provided by another user, I manage to fix the problem. I am putting this answer here for future reference for community.
def gatherStats(template_file, csv_file):
for lang in getLanguageCodes(csv_file):
lang_dir = os.path.join(template_file, lang)
try:
for filename in os.listdir(lang_dir):
path = os.path.join(lang_dir, filename)
if re.search(r'-.+-template-users-data.csv$',filename):
with open(path, 'rb') as template_user_data_file:
reader = csv.reader(template_user_data_file)
try:
for row in reader:
print row
except csv.ERROR as e:
logging.error(e)
else:
print "didn't find the file"
except Exception, e:
logging.exception(e)