Having Trouble Loading a Pickle File - python

I am trying to create a small game for fun, and I want to save and load previous run scores. I started a test file to mess around and try to figure out how pickling works. I have a pickle file with a small set of number. How do I add numbers to the pickle file and save it for the next run.
Currently I have it like this:
new_score = 9
filename = "scoreTest.pk"
outfile = open(filename,'wb')
infile = open(filename,'rb')
with infile as f:
scores = pickle.load(f)
scores.add(new_score)
pickle.dump(scores, outfile)
When I run it like this I get this error:
EOFError: Ran out of input
If someone could please tell me what is wrong and how to do it correctly that would be great. Apologies for any un-optimal code, I'm new to code.


You are trying to juggle a reader and writer on the same file at the same time. The open(filename, 'wb') of the write deletes whatever happened to be in the file so there is no data for the reader. You should only open the file when you really need to use it. And its better to write to a temporary file and rename it. If something goes wrong you haven't lost your data.
import pickle
import os
new_score = 9
filename = "scoreTest.pk"
tmp_filename = "scoreTest.tmp"
try:
with open(filename, 'rb') as infile:
scores = pickle.load(f)
except (IOError, EOFError) as e:
scores = default # whatever that is
scores.add(new_score)
with open(tmp_filename, 'wb') as outfile:
pickle.dump(scores, outfile)
os.rename(tmp_filename, filename)

Related

Unable to load file via pickle

I am using an example program from github in which it has imported pickle module at the beginning. But when it is trying to open file via pickle. Its giving an error
I can't understand the reason of it.
file = open('df_train_train', 'rb')
df_train_train = pickle.load(file)
file.close()
file = open('df_train_test', 'rb')
df_train_test = pickle.load(file)
file.close()
screen shot of my result.

You need to dump it first, then load it. Try the following:
# dump df_train_train
file = open('df_train_train', 'wb')
pickle.dump(df_train_train, file)
file.close()
Then
file = open('df_train_train', 'rb')
df_train_train = pickle.load(file)
file.close()

How to write rows in CSV file DYNAMICALLY in python?

I want to create a csv file and write data to it dynamically my script have to keep running 24/7 and csv files have to be created and written every 24 hours, right now all files are created when the program ends.
with open(file_name, 'r+') as f:
myDataList = f.readlines()
nameList = []
for line in myDataList:
entry = line.split(',')
nameList.append(entry[0])
if name not in nameList:
now = datetime.datetime.now()
dtString = now.strftime('%H:%M:%S')
writer = csv.writer(f)
writer.writerow(name, dtString)
Thanks in advance

Remove the file context. Use the earlier way of writing file. And keep doing flush() and fsync() on the file like shown below. That ensures that data is written to the file on disk.
f = open(FILENAME, MODE)
f.write(data)
f.write(data)
f.flush() #important part
os.fsync(f) # important part
For more info: see this link

How to edit and repickle?

From what I understand, the only way to edit an object in a pickle file is to unpickle each object, edit the desired object, and repickle everything back into the original file.
This is what I tried doing:
pickleWrite = open(fileName, 'wb')
pickleRead = open(fileName, 'rb')
#unpickle objects and put it in dataList
dataList = list()
try:
while True:
dataList.append(pickle.load(pickleRead))
except EOFError:
pass
#change desired pickle object
dataList[0] = some change
#clear pickle file
pickleWrite.truncate(0)
#repickle each item in data list
for data in dataList:
pickle.dump(data, fileName)
For some reason, this makes the pickle file have some large number of unknown symbols at the front of the file making it unpickleable.
Error when we try to unpickle:
_pickle.UnpicklingError: invalid load key, '\x00'.

I would suggest avoiding to create multiple opened connection to the same file like this.
Instead, you can try:
# Read the contents
with open(filename, 'rb') as file:
dataList = pickle.load(file)
# something to dataList
# Overwrite the picle file
with open(filename, 'wb') as file:
pickle.dump(dataList, file)

Python code to move file over socket

SO family, I trying to write an application where i can transfer files between two computers. I currently this working using something like this:
On client side
file = open(srcfile, 'r')
content = file.read()
file.close()
send_message(srcfile)
send_message(content)
On Server side:
filename = receive_message(message)
content = receive_message(message)
file = open(filename, 'w')
file.write(content)
file.close()
This seems to work for text files, but for other file types it doesn't work..
I'm thinking there has to be a better way. Any suggestions?

you need to use
file = open(srcfile, 'rb')
and
file = open(srcfile, 'wb')
respectivly ... the b means binary...

Replace and overwrite instead of appending

I have the following code:
import re
#open the xml file for reading:
file = open('path/test.xml','r+')
#convert to string:
data = file.read()
file.write(re.sub(r"<string>ABC</string>(\s+)<string>(.*)</string>",r"<xyz>ABC</xyz>\1<xyz>\2</xyz>",data))
file.close()
where I'd like to replace the old content that's in the file with the new content. However, when I execute my code, the file "test.xml" is appended, i.e. I have the old content follwed by the new "replaced" content. What can I do in order to delete the old stuff and only keep the new?

You need seek to the beginning of the file before writing and then use file.truncate() if you want to do inplace replace:
import re
myfile = "path/test.xml"
with open(myfile, "r+") as f:
data = f.read()
f.seek(0)
f.write(re.sub(r"<string>ABC</string>(\s+)<string>(.*)</string>", r"<xyz>ABC</xyz>\1<xyz>\2</xyz>", data))
f.truncate()
The other way is to read the file then open it again with open(myfile, 'w'):
with open(myfile, "r") as f:
data = f.read()
with open(myfile, "w") as f:
f.write(re.sub(r"<string>ABC</string>(\s+)<string>(.*)</string>", r"<xyz>ABC</xyz>\1<xyz>\2</xyz>", data))
Neither truncate nor open(..., 'w') will change the inode number of the file (I tested twice, once with Ubuntu 12.04 NFS and once with ext4).
By the way, this is not really related to Python. The interpreter calls the corresponding low level API. The method truncate() works the same in the C programming language: See http://man7.org/linux/man-pages/man2/truncate.2.html

file='path/test.xml'
with open(file, 'w') as filetowrite:
filetowrite.write('new content')
Open the file in 'w' mode, you will be able to replace its current text save the file with new contents.

Using truncate(), the solution could be
import re
#open the xml file for reading:
with open('path/test.xml','r+') as f:
#convert to string:
data = f.read()
f.seek(0)
f.write(re.sub(r"<string>ABC</string>(\s+)<string>(.*)</string>",r"<xyz>ABC</xyz>\1<xyz>\2</xyz>",data))
f.truncate()

import os#must import this library
if os.path.exists('TwitterDB.csv'):
os.remove('TwitterDB.csv') #this deletes the file
else:
print("The file does not exist")#add this to prevent errors
I had a similar problem, and instead of overwriting my existing file using the different 'modes', I just deleted the file before using it again, so that it would be as if I was appending to a new file on each run of my code.

See from How to Replace String in File works in a simple way and is an answer that works with replace
fin = open("data.txt", "rt")
fout = open("out.txt", "wt")
for line in fin:
fout.write(line.replace('pyton', 'python'))
fin.close()
fout.close()

in my case the following code did the trick
with open("output.json", "w+") as outfile: #using w+ mode to create file if it not exists. and overwrite the existing content
json.dump(result_plot, outfile)

Using python3 pathlib library:
import re
from pathlib import Path
import shutil
shutil.copy2("/tmp/test.xml", "/tmp/test.xml.bak") # create backup
filepath = Path("/tmp/test.xml")
content = filepath.read_text()
filepath.write_text(re.sub(r"<string>ABC</string>(\s+)<string>(.*)</string>",r"<xyz>ABC</xyz>\1<xyz>\2</xyz>", content))
Similar method using different approach to backups:
from pathlib import Path
filepath = Path("/tmp/test.xml")
filepath.rename(filepath.with_suffix('.bak')) # different approach to backups
content = filepath.read_text()
filepath.write_text(re.sub(r"<string>ABC</string>(\s+)<string>(.*)</string>",r"<xyz>ABC</xyz>\1<xyz>\2</xyz>", content))

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