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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 .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
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what is biological synthesis of nanoparticles
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Source:  OpenStax, Itse 1359 introduction to scripting languages: python. OpenStax CNX. Jan 22, 2016 Download for free at https://legacy.cnx.org/content/col11713/1.32
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