Python Reading numbers from text file

Question

I know this is a simple question, but I am extremely stuck.

file=open("record.txt","w+")
record = file.read()
print("The record is "+str(record)+"!!")

main code... 
file.write(str(reaction)) 
file.close()

I have got his code and I've got a number of 0.433534145355 in the file, but when I do the command of print the +str(record)+, it only comes up with The record is !! and the number is not there. What is wrong with this code. Is there a special code with decimal places, and I do not want to use int().

There is nothing in record when I do print() although I'm reading from a file which has a number in it — Masa Tono
– Masa Tono, Commented Oct 11, 2015 at 14:05

Community · Accepted Answer · 2017-05-23 11:52:08Z

6

As it says here:

'w+' Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the file.

so yes, your file is also opened for reading, but it is truncated (i.e. it is now zero bytes long, it's empty), leaving nothing left to read of what was there already.

Essentially, the w in 'w+' means the mode is orientated to writing, giving you the option to read as well (useful in those cases when you need to seek back and read what you have written. There will be nothing to read unless you write)

Instead you can use:

'r+' Open for reading and writing. The stream is positioned at the beginning of the file.

In this case, the r in 'r+' signifies the mode is orientated to reading, giving you the option to seek and write where necessary (useful when data is present already, but might need to be changed)

edited May 23, 2017 at 11:52

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answered Oct 11, 2015 at 14:15

Pynchia

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3 Comments

Padraic Cunningham Over a year ago

plus 1 for explaining what is actually causing the issue

Padraic Cunningham Over a year ago

Worth pointing out that w+ is only really useful if you want to seek back and read after writing. It will always truncate so there will be nothing to read unless you write

Pynchia Over a year ago

@PadraicCunningham done, thank you for the suggestion

Karoly Horvath · Accepted Answer · 2015-10-11 14:07:28Z

0

If you want to read from a file, you have to open it for reading too (r).

answered Oct 11, 2015 at 14:07

Karoly Horvath

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4 Comments

Masa Tono Over a year ago

But I though that w+ opens it for writing and reading if I read correctly from websites

Padraic Cunningham Over a year ago

@MasaTono, r+ is for reading and writing, if you want to add data use a

Pynchia Over a year ago

w+: Open for reading and writing. The file is created if it does not exist, otherwise it is truncated.

PM 2Ring Over a year ago

What Pynchia said. See stackoverflow.com/a/1466036/4014959 for descriptions of all the (standard) file modes that Python inherits from C.

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