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")
Related
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
Suppose I want to introduce a try-except block while handling a txt file. Which of the two following way of capturing the possible exception is correct?
try:
h = open(filename)
except:
h.close()
print('Could not read file')
try:
h = open(filename)
except:
print('Could not read file')
In other words, should the h.close() be called even if the exception occurs or not?
Secondly, suppose that you have the following code
try:
h = open(filename)
"code line here1"
"code line here2"
except:
h.close()
print('Could not read file')
If an error occurs in "code line here1", should I use h.close() in the except block?
Is there a difference with the previous coding lines?
You should use with, it will close the file appropriately:
with open(filename) as h:
#
# do whatever you need...
#
# when you get here, the file will be closed automatically.
You can enclose that in a try/except block if needed. The file will always be properly closed:
try:
with open(filename) as h:
#
# do whatever you need...
#
except FileNotFoundError:
print('file not found')
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)
So I am loading in a textfile with many different JSON file pathnames. There will be some instances where the JSON format might be invalid. I figured out a way to check if a file has invalid JSON, but I need it to display which specific file name is incorrect. Here is what my code looks like:
def openfile():
user_path= input("Please input file name:")
with open(user_path, 'r') as f:
for line in f:
strip= line.rstrip()
with open(strip, 'r') as x:
alpha = x.read()
try:
jObject = json.loads(alpha)
except ValueError as e:
print("There is invalid json %s" % e)
if __name__ == '__main__':
jsonparse()
Any help is greatly appreciated. Thanks!