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Open a text file for writing

Listing 1 calls the built-in function named open to create and return a file object in write mode . The reference to the file object is stored in the variable named theFile . The write mode is indicated by the "w" as the second parameter to the open function. The description of the open function at The Python Standard Library -- 2. Built-in Functions describes eight different modes that can be specified when a file object is created. The program in this module will use the following three modes:

  • 'w' -- open for writing, truncating the file first
  • 'r' -- open for reading (default)
  • 'a' -- open for writing, appending to the end of the file if it exists
Listing 1 . Open a text file for writing.
#Open a file object for writing. theFile = open("SampleTextFile.txt","w")

Write text and close the file

Listing 2 calls the write method five times in succession to write five strings into the file.

Listing 2 . Write text and close the file.
#Write several lines of text to the file. Note the requirement to explicitly #provide the newline at the end of each line of text.theFile.write("This is a sample text file.\n") theFile.write("Second line of text.\n")theFile.write("Third line.\n") theFile.write("Fourth line.\n")theFile.write("Last line.\n") #Be sure to close the filetheFile.close()

Once you have a file object, there are a variety of methods that you can call on that object, one of which is the method named write . The best description that I could find for that set of methods is located at File Objects , which is part of the documentation for Python version 2.3. (Hopefully it is still correct for Python version 3.)

That document provides the following description for the write method:

Write a string to the file. There is no return value. Due to buffering, the string may not actually show up in the file until the flush() or close() method is called.

Listing 2 calls the close method on the file after the strings are written to the file to ensure that the data is actually moved from the output buffer intothe file. The description of the close method at File Object reads as follows:

Close the file. A closed file cannot be read or written any more. Any operation which requires that the file be open will raise a ValueError after the file has been closed. Calling close() more than once is allowed.

Read and print the file contents with a for loop

Listing 3 shows one way to read the contents of a text file, line-by-line, using a for loop as an iterator. Note that the "r" mode is the default but it is shown here for clarity.

Listing 3 . Read and print the file contents with afor loop.
#Open the file object in read mode. theFile = open("SampleTextFile.txt","r")#Read and print the lines of text. for line in theFile:print(line,end='') #Close the filetheFile.close()

The output produced by the code in Listing 3 is shown in Figure 1 . As you can see, the output matches the text written into the file in Listing 2 .

Figure 1 . Output from the code in Listing 3.
This is a sample text file. Second line of text.Third line. Fourth line.Last line.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
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