I tried running the following program:
for i in range(5):
print(i, end=' ')
However, it waits for me to write some string in the next line and gives the output like:
0 1 2 3 4 'Hi'
where 'Hi' is what I input. I'm using the latest version 3.6.5 and can't seem to understand the reason behind this error. Can anyone help?
The default value for end is '\n', meaning that print() will write a newline character after printing the arguments. This would put the cursor on the next line.
Usually, stdout (to which print() writes by default) is also line buffered, meaning that data written to it is not flushed (and shown on your terminal) until a newline character is seen, to signal the end of the line.
You replaced the newline with a space, so no newline is written; instead a space is written, letting you write successive numbers one after the other on the same line.
Add an extra, empty print() call after your for loop to write the newline after looping:
for i in range(5):
print(i, end=' ')
print()
You could also add flush=True to the print(..., end=' ') calls to explicitly flush the buffer.
Alternatively, for a small enough range(), pass in the values to print() as separate arguments, leaving end at the default. Separate arguments are separated by the sep argument, by default set to a space:
print(*range(5))
The * in front of the range() object tells Python to loop over the range() object and pass all values that produces as separate arguments to the print() call; so all 5 numbers are printed with spaces in between and a newline character at the end:
>>> print(*range(5))
0 1 2 3 4
Related
I was wondering what the comma in the middle of print is used for?
This code:
print('No. of lower case letters : ', d['lower'])
A bit of history
Since Python 3, there is actually no print statement. Print is a function just like any other (In the now obsolete Python 2, print was indeed actually a statement).
A special case in Python 2 is that you could indeed have a comma at the end, such like
print "my string",
This would print the string with a space rather than a line feed as the terminator, allowing multiple print statements to contribute to one line. But forget about all this now, Python 2 is long gone (well, since January 2020).
Now to your question.
All functions in Python accept a number of arguments separated by a comma. The print function is no different. The print function takes any number of positional arguments, as well as a number of well-known named arguments, e.g.
print(a,b,c, file=f)
will send the positional arguments a, b and c and the keyword argument file. The print function will concatenate all positional arguments (separated by space) when printing them (optionally to the file specified by the file argument, otherwise to standard output).
The comma let's you add multiple arguments to the print statement. It basically lets you print them in succession, separated by a space.
Example:
print('hi', 'hello', 'greetings')
#hi hello greetings
The comma will let you print multiple strings in one calling of the print function. By default, each string will be separated by a space.
These are the arguments for the print function:
print(*objects, sep=' ', end='\n', file=sys.stdout)
You can change the sep argument to something else.
I have the following code when writing to a text file:
def writequiz(quizname,grade,perscore,score,username):
details=[quizname,username,grade,perscore,score]
with open('quizdb','a') as userquiz:
print(details,file=userquiz)
Now the code is doing what I want it to (writing to a new line every time), however if I wanted to write every list to the same line in the text file how would I do this using the print method as used above? I know I could use file.write, but how do I remove the newline character in the print statement? Slightly hypothetical but it was bugging me.
If you are using python 2.x, you can do the following:
print >> userquiz, details, # <- notice the comma at the end
If using pytnon 3.x, you can do this:
print(details,file=userquiz, end = " ")
Check print documentation.
You can set the end parameter of print to be an empty string (or some other character):
print(details, file=userquiz, end='')
From the docs, you can see that it defaults to a newline:
print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)
Print objects to the text stream file, separated by sep and followed by end. sep, end, file and flush, if present, must be given
as keyword arguments.
This is what is being printed to the file currently.
In python3 print('\n') will generate an extra blank line. Could someone make a brief explanation about this?
Thanks in advance.
In the documentation for print it is stated that:
All non-keyword arguments are converted to strings like str() does and written to the stream, separated by sep and followed by end.
The default value for end is '\n', so Python first prints the supplied '\n' and then end which equals '\n' too; that's why you see two blank lines.
Change the default value if you don't want that:
print('\n', end='')
Note that this also applies to Python 2.x's print statement, it also writes '\n' at the end. You can change the behavior there by appending a comma character.
I'm trying to print multiple characters on one line with a delay between each, in Python. I'm using v3.5.
This is what I've been trying to do:
import time
for i in range(30):
print("-",end='')
time.sleep(.5)
Looking at it, I would expect "-" to be printed 30 times, with .5 second delay between each "-". This would all be on one line. When I tried this, the program would seemingly "freeze" by doing nothing for 15 or so seconds. During this time, I'm sure the program is going through this loop, but the "-"s are all printed simultaneously after the time is up.
This is because of end=' ', correct? Is there a simple workaround?
Add flush=True so the output is not buffered:
import time
for i in range(30):
print("-",end='', flush=True)
time.sleep(.5)
There's (line) buffering for the output, add sys.stdout.flush() to your loop.
This is because of buffering: the system doesn't print things until it gets a newline or the buffer fills up. I don't have v3 here, but I think that inserting a flush operation should fix the problem.
import time, sys
for i in range(30):
print("-", end="")
sys.stdout.flush()
time.sleep(.5)
I effortlessly reproduced the behavior with ipython3 in Gnome Terminal. Then I looked at help(print) and added a parameter to the print command. Guess which one?
print(...)
print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
Prints the values to a stream, or to sys.stdout by default.
Optional keyword arguments:
file: a file-like object (stream); defaults to the current sys.stdout.
sep: string inserted between values, default a space.
end: string appended after the last value, default a newline.
flush: whether to forcibly flush the stream.
This code is from http://docs.python.org/2/tutorial/errors.html#predefined-clean-up-actions
with open("myfile.txt") as f:
for line in f:
print line,
What I don't understand is what's that , for at the end of print command.
I also checked doc, http://docs.python.org/2/library/functions.html#print.
Not understanding enough, is it a mistake?(it seems not. it's from the official tutorial).
I am from ruby/javascript and it's unusual for me.
In python 2.7, the comma is to show that the string will be printed on the same line
For example:
for i in xrange(10):
print i,
This will print
1 2 3 4 5 6 7 8 9
To do this in python 3 you would do this:
for i in xrange(10):
print(i,end=" ")
You will probably find this answer helpful
Printing horizontally in python
---- Edit ---
The documentation, http://docs.python.org/2/reference/simple_stmts.html#the-print-statement, says
A '\n' character is written at the end, unless the print statement ends with a comma.
It prevents the print from ending with a newline, allowing you to append a new print to the end of the line.
Python 3 changes this completely and the trailing comma is no longer accepted. You use the end parameter to change the line ending, setting it to a blank string to get the same effect.
From Python trailing comma after print executes next instruction:
In Python 2.x, a trailing , in a print statement prevents a new line to be emitted.
The standard output is line-buffered. So the "Hi" won't be printed before a new line is emitted.
in python 2.7:
print line,
in python 3.x:
print(line, end = ' ')