This question already has answers here:
How do I append to a file?
(13 answers)
Closed 8 years ago.
I need to add my program's outputs to a saved file every time I run the program without overwriting the previous outputs.
This is how I'm writing to a file now:
lead.write(str(alldates))
Any ideas?
Here, you should open the file in append mode:
append_text = str(alldates)
with open('my_file.txt', 'a') as lead:
lead.write(append_text)
There are lots of specialised ways to open files for different purposes, and you can read about them in the documentation.
You should open the file in append mode.
Related
This question already has answers here:
Confused by python file mode "w+" [duplicate]
(11 answers)
Closed 6 months ago.
I am using VSC for writing python scripts to read/write file. I am able to write file using the below code:
with open("score_card.txt", mode="w+") as file_data:
file_data.write("23")
but when trying to read the file using the below code:
with open("score_card.txt", mode="w+") as file_data:
print(file_data.read())
it is not giving anything in the terminal.
You need to open the file in read mode. Here's an example:
with open("score_card.txt", mode="r") as file_data:
print(file_data.read())
You can learn more about the open function modes here https://docs.python.org/3/library/functions.html#open
An important thing to remember is that the w+ mode is for truncating and writing. This means that it will wipe the file contents, so when you try to read it, there is nothing in the file. You should use mode='r' on all files that you don't intend to edit.
This question already has answers here:
read the whole file at once
(2 answers)
Closed 7 months ago.
Let us say I wanted to read a whole file at once instead of going through it line by line (let's say for example to speed up retrieval of the times 'i' occurs in the file). How would I go about reading it as a whole instead of the lines in which it is written?
with open("file.ext", 'r') as f:
data = f.read()
As others have mentioned, you can find an official Python tutorial for Reading and Writing Files which explains this. You can also see the Methods of File Objects section, which explains the use of f.read(size) and f.readline() and the difference between between them.
This question already has answers here:
Is there a need to close files that have no reference to them?
(6 answers)
Closed 1 year ago.
In python, if i opened a file:
file = open('file.txt','r')
// read the file and stuff
file = None // does this close the file and free up resources?
then set it to something else, would that file be closed? would there be any downsides to doing this?
I am aware that 'file.close()' does this, but i want to know if i can just set it to something else instead.
You should always close the file every time you open it unless you are using with open.
This question already has an answer here:
Python - Store variables in a list that save each time program restarts [duplicate]
(1 answer)
Closed 1 year ago.
So I know the .append function adds elements to a list. But that only works as long as the script is running. If I rerun the file, the list is back to its previous state with no changes made. Is there a way to save the changes?
You can save the list to a file after everything is done:
Here for a+ mode:
All file handling modes <---Here
a+: Open for reading and appending (writing at end of file). The file is created if it does not exist.
with open('test_file','a+') as file:
lst=[...]
....
file.write(lst)
This question already has answers here:
How do I append to a file?
(13 answers)
Closed 5 years ago.
I have a function which prints messages. then I want to save this messages into a file. But when I use .write(function parameter) it only write last message inside my file
writing_in_log = True
def print_and_log(message):
if write_in_log is True:
logFile = open("log", "w+")
logFile.write(message)
logFile.close()
I suppose you are not using the 'a' parameter when opening the file:
with open('file.txt', 'a') as file:
file.write('function parameter')
You probably open the file for each writing with open(yourfile, 'w') which will erase any content from the file before you write to it. If you want to append to your file, use open(yourfile, 'a').
In case this is not the error we need more information about what you are doing, i.e. the relevant parts of the code.