This question already has answers here:
Difference between modes a, a+, w, w+, and r+ in built-in open function?
(9 answers)
Closed 1 year ago.
When you open file like that:
f = open("demofile.txt", "r")
f.write("Something")
There are some in which you can open file.
"r" Opens a file for reading only.
"r+" Opens a file for both reading and writing.
"rb" Opens a file for reading only in binary format.
"rb+" Opens a file for both reading and writing in binary format.
"w" Opens a file for writing only.
"a" Open for writing. The file is created if it does not exist.
"a+" Open for reading and writing. The file is created if it does not exist.
"x" Creates a new file. If file already exists, the operation fails.
"t" This is the default mode. It opens in text mode.
"b" This opens in binary mode.
"+" This will open a file for reading and writing (updating)
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.
I have a script which I use for requesting data from an external API. My script contains complex logic and describing it will take much time. At a certain point of my script I need to open a file, loop over it and and extract each value from it.
with open(os.path.abspath("/data/data/com.termux/files/home/storage/forecast/endpoints/leagueIdExtracted.txt"), "r+") as leagueIdExtracted:
print("Check is file {} was opened".format(leagueIdExtracted))
for id in leagueIdExtracted:
print("ID {} from opened file".format(id))
savedLeagues.add(int(str(id[:-1])))
print("League IDs {} from file which contain alredy requested IDs".format(savedLeagues))
But sometimes isn't up to me file which i open in above isn't exist
with open(os.path.abspath("/data/data/com.termux/files/home/storage/forecast/endpoints/leagueIdExtracted.txt"), "r+") as leagueIdExtracted:
Because of it while I open this file I have to open it in "w+" mode. Opening it in "w+" guarantees that a non-existing file will be created and opened. But while my script opened the file in "w+" mode it can't extract values from it.
for id in leagueIdExtracted:
print("ID {} from opened file".format(id))
savedLeagues.add(int(str(id[:-1])))
Because of it I have to manually switch between "w+" and "r" modes. Can anyone advise me whether Python has a mode which will create file while opening it if it does not exist as "w+" mode and also allow to extract data as
"r" mode?
You can use a+ as a mode. Using a+ opens a file for both appending and reading. If the file doesn't exist, it will be created.
# In this example, sample.txt does NOT exist yet
with open("sample.txt", "a+") as f:
print("Data in the file: ", f.read())
f.write("wrote a line")
print("Closed the file")
with open("sample.txt", "a+") as f:
f.seek(0)
print("New data in the file:", f.read())
Output:
Data in the file:
Closed the file
New data in the file: wrote a line
You should keep in mind that opening in a+ mode will place the cursor at the end of the file. So if you want to read data from the beginning, you will have to use f.seek(0) to place the cursor at the start of the file.
You want to use 'r+' if your objective is to read/write to existing files. In case you want to create new file as well, use 'a+'. In other words you will be able to do all of the follwing three.
1. Create if file does not exist
2. Write (append) if file exists
3. Read in file
Quoting from Reading and Writing Files: Python Documentation:
'r' when the file will only be read,
'w' for only writing (an existing file with the same name will be erased),
'a' opens the file for appending; any data written to the file is automatically added to the end.
'r+' opens the file for both reading and writing.
I have this code:
line1 = []
line1.append("xyz ")
line1.append("abc")
line1.append("mno")
file = open("File.txt","w")
for i in range(3):
file.write(line1[i])
file.write("\n")
for line in file:
print(line)
file.close()
But when I try it, I get an error message like:
File "...", line 18, in <module>
for line in file:
UnsupportedOperation: not readable
Why? How do I fix it?
You are opening the file as "w", which stands for writable.
Using "w" you won't be able to read the file. Use the following instead:
file = open("File.txt", "r")
Additionally, here are the other options:
"r" Opens a file for reading only.
"r+" Opens a file for both reading and writing.
"rb" Opens a file for reading only in binary format.
"rb+" Opens a file for both reading and writing in binary format.
"w" Opens a file for writing only.
"a" Open for writing. The file is created if it does not exist.
"a+" Open for reading and writing. The file is created if it does not exist.
Use a+ to open a file for reading, writing and create it if it doesn't exist.
a+ Opens a file for both appending and reading. The file pointer is at
the end of the file if the file exists. The file opens in the append
mode. If the file does not exist, it creates a new file for reading
and writing. -Python file modes
with open('"File.txt', 'a+') as file:
print(file.readlines())
file.write("test")
Note: opening file in a with block makes sure that the file is properly closed at the block's end, even if an exception is raised on the way. It's equivalent to try-finally, but much shorter.
There are few modes to open file (read, write etc..)
If you want to read from file you should type file = open("File.txt","r"), if write than file = open("File.txt","w"). You need to give the right permission regarding your usage.
more modes:
r. Opens a file for reading only.
rb. Opens a file for reading only in binary format.
r+ Opens a file for both reading and writing.
rb+ Opens a file for both reading and writing in binary format.
w. Opens a file for writing only.
you can find more modes in here
This will let you read, write and create the file if it don't exist:
f = open('filename.txt','a+')
f = open('filename.txt','r+')
Often used commands:
f.readline() #Read next line
f.seek(0) #Jump to beginning
f.read(0) #Read all file
f.write('test text') #Write 'test text' to file
f.close() #Close file
Sreetam Das's table is nice but needs a bit of an update according to w3schools and my own testing. Unsure if this due to the move to python 3.
"a" - Append - will append to the end of the file and will create a file if the specified file does not exist.
"w" - Write - will overwrite any existing content and will create a file if the specified file does not exist.
"x" - Create - will create a file, returns an error if the file exist.
I would have replied directly but I do not have the rep.
https://www.w3schools.com/python/python_file_write.asp
I have this code:
line1 = []
line1.append("xyz ")
line1.append("abc")
line1.append("mno")
file = open("File.txt","w")
for i in range(3):
file.write(line1[i])
file.write("\n")
for line in file:
print(line)
file.close()
But when I try it, I get an error message like:
File "...", line 18, in <module>
for line in file:
UnsupportedOperation: not readable
Why? How do I fix it?
You are opening the file as "w", which stands for writable.
Using "w" you won't be able to read the file. Use the following instead:
file = open("File.txt", "r")
Additionally, here are the other options:
"r" Opens a file for reading only.
"r+" Opens a file for both reading and writing.
"rb" Opens a file for reading only in binary format.
"rb+" Opens a file for both reading and writing in binary format.
"w" Opens a file for writing only.
"a" Open for writing. The file is created if it does not exist.
"a+" Open for reading and writing. The file is created if it does not exist.
Use a+ to open a file for reading, writing and create it if it doesn't exist.
a+ Opens a file for both appending and reading. The file pointer is at
the end of the file if the file exists. The file opens in the append
mode. If the file does not exist, it creates a new file for reading
and writing. -Python file modes
with open('"File.txt', 'a+') as file:
print(file.readlines())
file.write("test")
Note: opening file in a with block makes sure that the file is properly closed at the block's end, even if an exception is raised on the way. It's equivalent to try-finally, but much shorter.
There are few modes to open file (read, write etc..)
If you want to read from file you should type file = open("File.txt","r"), if write than file = open("File.txt","w"). You need to give the right permission regarding your usage.
more modes:
r. Opens a file for reading only.
rb. Opens a file for reading only in binary format.
r+ Opens a file for both reading and writing.
rb+ Opens a file for both reading and writing in binary format.
w. Opens a file for writing only.
you can find more modes in here
This will let you read, write and create the file if it don't exist:
f = open('filename.txt','a+')
f = open('filename.txt','r+')
Often used commands:
f.readline() #Read next line
f.seek(0) #Jump to beginning
f.read(0) #Read all file
f.write('test text') #Write 'test text' to file
f.close() #Close file
Sreetam Das's table is nice but needs a bit of an update according to w3schools and my own testing. Unsure if this due to the move to python 3.
"a" - Append - will append to the end of the file and will create a file if the specified file does not exist.
"w" - Write - will overwrite any existing content and will create a file if the specified file does not exist.
"x" - Create - will create a file, returns an error if the file exist.
I would have replied directly but I do not have the rep.
https://www.w3schools.com/python/python_file_write.asp
This question already has answers here:
Difference between modes a, a+, w, w+, and r+ in built-in open function?
(9 answers)
Closed 9 years ago.
As in, when opening a file with open(), why do we have modes 'r+', 'w+', 'a+'? Surely mode 'a' does the same job? I'm especially confused by the difference between modes 'a' and 'a+' - could someone explain where they differ and, if possible, when one should use one or the other?
The opening modes are exactly the same that C fopen() std library function.
The BSD fopen manpage defines them as follows:
``a'' Open for writing. The file is created if it does not exist. The
stream is positioned at the end of the file. Subsequent writes
to the file will always end up at the then current end of file,
irrespective of any intervening fseek(3) or similar.
``a+'' Open for reading and writing. The file is created if it does not
exist. The stream is positioned at the end of the file. Subse-
quent writes to the file will always end up at the then current
end of file, irrespective of any intervening fseek(3) or similar.
The only difference between a and a+ is that a+ allows reading of files.
See this post for more info.
Quoted from the Python 2.7 tutorial:
mode can be 'r' when the file will only be read, 'w' for only writing
(an existing file with the same name will be erased), and 'a' opens
the file for appending; any data written to the file is automatically
added to the end. 'r+' opens the file for both reading and writing.
The mode argument is optional; 'r' will be assumed if it’s omitted.
'a' opens the file in write (append at end of file) mode, while 'r+' opens it in both read and write (insert at start of file).