I want to print the characters in a line one at a time. What this code ends up doing is reading the entire line one character at a time (with a pause between each character, so I know it is iterating through the characters correctly) then when it finishes that line, it will print all of the characters at once.
for line in lines:
for ch in line:
print(ch, end = ' ')
os.system("pause")
However, if I do:
for line in lines:
for ch in line:
print(ch, end = '\n') #same effect as print(ch)
os.system("pause")
it will print one character with a newline, then a system pause.
Why will it not print correctly in the first scenario but work in the second?
Also, I just ran a random test:
print ("is", end=' ')
os.system("pause")
print("newline?")
It did not print my message until after the system pause. Why did it not print "is" before the pause? It seems like there is some hidden workings of the print() function than I am not understanding. Anyone have some explanations?
Your output is being buffered: the output is held until a newline is sent, because printing a single line all at once is more efficient than printing it a character at a time.
You can put sys.stdout.flush() after each print() if you like. Other solutions here. Personally I kinda like the wrapper one. You can combine that with a context manager that sets and restores stdout in a with block for maximum Pythonicity.
Related
I am new to coding. And I would like to know if there's a way for input function to not print newline character after the value is entered. Something like print function's argument end. Is there any way?
Well, you can't make input() trigger by anything besides 'Enter' hit (other way may be using sys.stdin and retrieving character one-by-one until you receive some stop marker, but it's difficult both for programmer and for user, I suppose). As a workaround I can the suggest the following: if you can know the length of line written before + length of user input, then you can use some system codes to move cursor back to the end of previous line, discarding the printed newline:
print("This is first line.")
prompt = "Enter second: "
ans = input(prompt)
print(f"\033[A\033[{len(prompt)+len(ans)}C And the third.")
\033[A moves cursor one line up and \033[<N>C moves cursor N symbols right. The example code produces the following output:
This is first line.
Enter second: USER INPUT HERE And the third.
Also note that the newline character is not printed by your program, it's entered by user.
name=input('Enter your name : ')
print('hello',name,end='')
I know about the end function which is abov
I'm trying to print out a string with the end=\r to send the cursor back to beginning of the line, and overwrite the printed string using a for loop
This is the code thus far I got :
import time
print("░░░░░░░░░░░░░", end='\r')
for i in ("SECRET"):
print(i ,end='')
time.sleep(0.3)
Ideally, it should slowly overwrite some of the dotted pattern characters with characters from `"SECRET" every 0.3 seconds.
However, when run, the for loop instead iterates and prints characters on a single space, overwriting the characters it prints out itself, instead of advancing to the next available space, overwriting the dot pattern there and typing out the remaining characters in the string it iterates over
Removing the entire print statement associated with the dotted pattern characters allows the loop to function normally, printing out the string it iterates over properly, however, it is needed for the loop to print out the string and overwrite the dotted characters
Essentially, I want to overwrite some of the dotted pattern characters one by one using characters from the string the for loop iterates over, with the help of \r
I am on Ubuntu Studio
Screen output is line-buffered. This means that when you print something followed by a newline it appears on the screen immediately, but if you print something without a newline it might take a while to appear.
This is what's happening to you -- the output inside the for loop is not followed by a newline, so it doesn't appear onscreen immediately.
You can add flush=True to the print call to force the output to appear immediately instead of waiting:
print(i, end='', flush=True)
you can't overwrite characters in python.
you can, though, clear the whole screen by using os.system('cls') on windows or os.system('clear') on linux and unix.
here is the full code:
import time, os
output = '░░░░░░░░░░░░░'
for i in range(7):
print(output)
output = "SECRET"[:i]+output[i:]
time.sleep(0.3)
if os.name == 'nt': #on windows
os.system("cls")
else:
os.system("clear") #not on windows
print(output)
also, this will only work when you are not running from the shell and if you want to see the full output, write time.sleep(1) at the end.
I'm working on writing a simple Hangman game in Python from what I know so far (I'm doing Learn Python the Hard Way) and so far I have this:
from sys import argv
import random
script_name, dict_file = argv
hang_list = open(dict_file).read().splitlines()
hang_list = filter(None, hang_list)
word = random.choice(hang_list)
guesses = ''
def compare_words():
global guesses
new_word = ''
for char in word:
if char in guesses:
new_word += char
else:
new_word += "_"
return new_word
def test_letter():
global guesses
letter = raw_input("Guess a letter: ")
guesses += letter
new_word = compare_words()
print "\nCurrent guesses: %s" % guesses
print "%s\n\n" % new_word
if new_word == word:
print "You won!"
else:
test_letter()
test_letter()
I've yet to implement the scoring system (piece of cake) but I have an issue with the layout. As you can tell, this will print "Current guesses: " and the new word each time; however, what I want is four lines that look like:
Guess a letter:
Guesses: abczy
__c__b_
And have those three lines keep updating. However, I am having trouble figuring out how to make the print replace stdout. I believe I need to use the \r escape character, yet I've tried placing that in various places but can't get it to work. So, how should I modify this to get it to replace? I would prefer not to just clear, as then it still makes things a bit messy; I want to just replace what's there. Thanks!
It would be a bit tricky to make this work for all terminals, but if yours understands ANSI escape codes like mine does, this might work:
...
if new_word == word:
print "You won!"
else:
print '\033[F'*7
print ' '*17 + '\b'*17 + '\033[F'
test_letter()
This relies on the ANSI code F: move the cursor up one line; backspaces (\b) alone have no effect once the beginning of the line is reached.
The first print takes you back up to the input line and the second deletes the character that was previously entered.
You can use the escape characters \033c and this will erase the code in a terminal window and put the cursor at the top left.
For example this code:
import time
print("text 1")
time.sleep(1)
print('\033c')
time.sleep(1)
print("text 2")
This code will print "text 1" wait one second, clear the console, wait one second and then print "text 2".
So you could use the code
def test_letter():
print("\033c")
global guesses
letter = raw_input("Guess a letter: ")
guesses += letter
new_word = compare_words()
print "\nCurrent guesses: %s" % guesses
print "%s\n\n" % new_word
if new_word == word:
print "You won!"
else:
test_letter()
What this code will do is clear the console, ask the person to guess a number, display that four line piece of code that you wanted and then clear the console again.
I hope this helps!
If you want to replace the content of a specific line, from a specific position, you can use ANSI Escape Codes. To do this, make sure that you're using stdout.write() rather than print(). You can access this method by using the following import statement:
from sys import stdout
Then, in order to navigate the "cursor" (where text printed with this method will go), use the escape code \u001b[<L>;<C>H (or \u001b[<L>;<C>F where <L> and <C> represent the respective line number and character index of the desired position. For example, if you wanted to set the cursor to line 3; character 2, you would do the following.
stdout.write(u"\u001b[3;2H")
Note the u proceeding the double-quoted string. This is required in Python 2.x, since it contains special characters, but can be omitted in Python 3 and above.
Once you have set the cursor to be at the desired position, anything you write will replace the characters that currently reside there. This is important, because if the replacement string is shorter than the original, you may end up with trailing legacy characters. The simplest way to deal with this is to pad the printing string in spaces.
After doing this you should probably move the cursor back to the end of stdout, using the same method, and flush the output with stdout.flush().
Example
Let's say I had the following output on the terminal:
Name: Shakespeare
Score: 0
Some text...
I could change the score to 1 by running the following:
stdout.write(u"\u001b[2;8H")
stdout.write("1")
stdout.write(u"\u001b[5;0H")
stdout.flush()
Again, the u is optional in Python 3 and up.
Notes
This line-and-character-number method applies to all output currently being displayed in the terminal. This means that if you have anything left from another program or command, for example
$ python game.py
so it is best to clear the output at the start of your program, with something like print(u"\033c"), or os.system("clear"), otherwise you may end up writing to the wrong line.
Also, if your going to use stdout.write() anywhere else, remember to put \n at the end if you want to go to the next line.
The \r character is a carriage return, which means it will return the cursor to the start of the current line. That's OK if you want to redraw the line the cursor is on, but no good if you want to redraw other lines.
To do what you want, you need to use a terminal library like curses on Linux or the console API on Windows. If you are just working on Linux and want a simpler way to access colours, cursor movement and input without echo, you could do worse than try out blessed (https://pypi.python.org/pypi/blessed/).
If you need a cross platform API to do this sort of thing, there is no pure Python way to handle it all yet, but I am working on one. The Screen class in https://github.com/peterbrittain/asciimatics cover all the features above in a cross-platform manner.
I need to print over one line in a loop (Python 3.x). Looking around on SO already, I put this line in my code:
print('{0} imported\r'.format(tot),)
However, it still prints multiple lines when looped through. I have also tried
sys.stdout.write('{0} imported\r'.format(tot))
but this doesn't print anything to the console...
Anyone know what's going on with this?
If you want to overwrite your last line you need to add \r (character return) and end="" so that you do not go to the next line.
values = range(0, 100)
for i in values:
print ("\rComplete: ", i, "%", end="")
print ("\rComplete: 100%")
In the first case, some systems will treat \r as a newline. In the second case, you didn't flush the line. Try this:
sys.stdout.write('{0} imported\r'.format(tot))
sys.stdout.flush()
Flushing the line isn't necessary on all systems either, as Levon reminds me -- but it's generally a good idea when using \r this way.
I prefer to use the solution of Jan but in this way:
values = range(0, 101)
for i in values:
print ("Complete: ", i, "%", end="\r")
print ()
This question already has an answer here:
Why doesn't print output show up immediately in the terminal when there is no newline at the end?
(1 answer)
Closed last month.
I'm trying to create a progress bar in the terminal, by repeatedly printing # symbols on the same line.
When i tell Python to not add newlines - using print('#', end='') in Python 3 or print '#', in Python 2 - it prints as desired, but not until the whole function is finished. For example:
import time
i = 0
def status():
print('#', end='')
while i < 60:
status()
time.sleep(1)
i += 1
This should print '#' every second but it doesn't. It prints them all after 60 seconds. Using just print('#') prints it out every second as expected. How can I fix this?
You probably need to flush the output buffer after each print invocation. See How to flush output of Python print?
Python is buffering the output until a newline (or until a certain size), meaning it won't print anything until the buffer gets a newline character \n. This is because printing is really costly in terms of performance, so it's better to fill a small buffer and only print once in a while instead.
If you want it to print immediately, you need to flush it manually. This can be done by setting the flush keyword argument to True.
import time
word = "One letter at a time"
for letter in word:
print(letter, end='', flush=True)
time.sleep(0.25)
You can always use the strip() function.