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writing string variable to file

9 replies on 1 page. Most recent reply: Apr 1, 2019 3:29 PM by Gordon Blue

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alvin murphy

Posts: 4
Nickname: amurphy
Registered: Oct, 2004

writing string variable to file

Posted: Oct 19, 2004 4:45 PM

Hi: I am totally new, trying to learn. How do you write a string variable to a file? The following does not work, as you can see.

IDLE 1.0.2
>>> str_Name = "Doe-John"
>>> myfile = open("myfile", "w")
>>> myfile.write(str_Name)
>>> myfile.close
<built-in method close of file object at 0x00942360>
>>> myfile = open("myfile", "r")
>>> myfile.readline()
''
>>>

Thanks

Andy

Posts: 28
Nickname: adn
Registered: Jul, 2004

Re: writing string variable to file

Posted: Oct 20, 2004 2:00 AM

if you put a newline char on the end of the text;

myfile.write(str_name + '\n')

Then try again. I guess it's because readline expects a full line. Also call "myfile.close()" - myfile.close just shows you the .close method.

You can strip off the newline when you fetch the line back:

>>> myfile.readline()
'John Doe\n'
>>> _.rstrip() # ('_' is set to the last value)
'John Doe'

alvin murphy

Posts: 4
Nickname: amurphy
Registered: Oct, 2004

Re: writing string variable to file

Posted: Oct 20, 2004 2:19 PM

Thanks for your help. I am a total beginner; a little visual basic years ago. Eventually want to write a history taking program for psychiatry. So these are baby steps. Your solution works, but not in my Win Idle editor; i.e. if I write the code there and ask it to run the module, it does not work (the file and readline part). It works if I type it in the interpreter GUI. Do not understand that. Maybe I am "running" it wrong, i.e. maybe choosing "run module" is the wrong option.

Also do not understand your last line of code that strips the trailing \n. Could you help with that. Also is there a read command that reads all the text in there, not just a line? Thanks

Andy

Posts: 28
Nickname: adn
Registered: Jul, 2004

Re: writing string variable to file

Posted: Oct 21, 2004 2:20 AM

That's odd about the module not working. Post the relevant bits here for us to see.

As for the last bit of my code - Whenever you do something that returns a value and you don't assign it to something, it gets put in the variable "_" . Perhaps my example should have read:

>>> line = myfile.readline()
>>> line.rstrip()
'John Doe'

You can find the details about .rstrip() and other string methods here: http://docs.python.org/lib/string-methods.html

To read the entire contents of a file, use .read() rather than .readline()

alvin murphy

Posts: 4
Nickname: amurphy
Registered: Oct, 2004

Re: writing string variable to file

Posted: Oct 21, 2004 11:57 PM

Thanks for your answer. I am puzzled. My code works if I type it in line by line in the IDLE command line or the IDLE GUI or if I paste it in line by line from the IDLE editor. It does not run (successfully if I run it from the editor by selecting "run module" or from the gui or command line by using "import". I have tried it on three machines, one with Win XP, one with Win 2000, one with Win 98; same result. I have not yet tried it on my linux machine which is not working. I will try to paste the file in below. Thanks also for the other comments.


str_Name = raw_input("Please enter your name")
myfile = open("myfile", "w")
myfile.write(str_Name)
myfile.close()
str_PresentIllness = raw_input("Please describe your problem")
myfile = open("myfile", "a")
myfile.write(str_PresentIllness)
myfile.close()
myfile = open("myfile")
myfile.read()
myfile.close()
raw_input()

Andy

Posts: 28
Nickname: adn
Registered: Jul, 2004

Re: writing string variable to file

Posted: Oct 22, 2004 5:22 AM

I see... IDLE prints out the return value of a function if you don't assign it to something;

>>> myFunction()
'Blah'
>>> a = myFunction()
>>>

It's a feature for easy debugging I guess. But come normal execution, the return values are ignored, you have to explicitly display them.

Also:

- You can keep the file open and write both variables one after the other without closing the file each time.

- Think about seperating the two lines in the file with something.

alvin murphy

Posts: 4
Nickname: amurphy
Registered: Oct, 2004

Re: writing string variable to file

Posted: Oct 22, 2004 5:07 PM

Thanks for the tip about not having to close the file twice or each time I write to it. These are certainly baby steps, and I would never imagine a program that would write to a file and immediately read from it; I imagine the "reading" would occur much later, perhaps via word processor, with formatting etc.. Anyway I still do not understand your answer. Pardon if I use the wrong terminology, but I know my "write" statements are working because I can manually open myfile after the the little program has run and find the text; what I do not understand is why the "read" statement or command does not produce any text on the GUI screen when the whole thing is run as a module from the editor. in other words, it runs all the commands or statements including the raw_input, open, close, write, but not read. Thanks again.

Andy

Posts: 28
Nickname: adn
Registered: Jul, 2004

Re: writing string variable to file

Posted: Oct 23, 2004 5:27 AM

I meant;

print myfile.readline()

rather than just;

myfile.readline()

Selena Blane

Posts: 2
Nickname: sharlotta
Registered: Feb, 2019

Re: writing string variable to file

Posted: Feb 6, 2019 2:44 AM

String concatenation:

plot.savefig ('hanning' + str (num) + '.pdf')

Conversion qualifier:

plot.savefig ('hanning% s.pdf'% num)

Using local variable names:

plot.savefig ('hanning% (num) s.pdf'% locals ()) # Neat trick

Using format ():

plot.savefig ('hanning {0} .pdf'.format (num)) # Note: This is the new preferred way

Using f-lines:

plot.savefig (f'hanning {num} .pdf ') # added in Python 3.6

Using string.Template:

plot.savefig (string.Template ('hanning $ {num} .pdf'). substitute (locals ()))

Also look https://pro-papers.com

Gordon Blue

Posts: 1
Nickname: solange
Registered: Apr, 2019

Re: writing string variable to file

Posted: Apr 1, 2019 3:29 PM

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