write Python string object to file

Question

I have this block of code that reliably creates a string object. I need to write that object to a file. I can print the contents of 'data' but I can't figure out how to write it to a file as output. Also why does "with open" automatically close a_string?

with open (template_file, "r") as a_string:
   data=a_string.read().replace('{SERVER_NAME}', server_name).replace('{BRAND}', brand).replace('{CONTENT_PATH}', content_path).replace('{DAMPATH}', dampath).replace('{ENV}', env).replace('{CACHE_DOCROOT}', cache_docroot)

a_string.write(your_string_object) should work inside the with block — ZdaR
– ZdaR, Commented Dec 1, 2015 at 15:36
Do you want to write the string to the file or do you want to read the file and replace parts of the read string? — albert
– albert, Commented Dec 1, 2015 at 15:37
I need to read the template file into memory, make changes to it then write out the (changed) object to a new file. I do not want to edit the file "in place." — mr.zog
– mr.zog, Commented Dec 1, 2015 at 15:55

dsh · Accepted Answer · 2015-12-04 17:42:44Z

3

I can print the contents of 'data' but I can't figure out how to write it to a file as output

Use with open with mode 'w' and write instead of read:

with open(template_file, "w") as a_file:
   a_file.write(data)

Also why does "with open" automatically close a_string?

open returns a File object, which implemented both __enter__ and __exit__ methods. When you enter the with block the __enter__ method is called (which opens the file) and when the with block is exited the __exit__ method is called (which closes the file).

You can implement the same behavior yourself:

class MyClass:
    def __enter__(self):
        print 'enter'
        return self

    def __exit__(self, type, value, traceback):
        print 'exit'

    def a(self):
        print 'a'

with MyClass() as my_class_obj:
     my_class_obj.a()

The output of the above code will be:

'enter'
'a'
'exit'

edited Dec 4, 2015 at 17:42

dsh

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answered Dec 1, 2015 at 15:38

DeepSpace

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Comments

mr.zog · Accepted Answer · 2015-12-01 18:48:22Z

0

with open (template_file, "r") as a_string:
   data=a_string.read().replace('{SERVER_NAME}', server_name).replace('{BRAND}', brand).replace('{CONTENT_PATH}', content_path).replace('{DAMPATH}', dampath).replace('{ENV}', env).replace('{CACHE_DOCROOT}', cache_docroot).replace('{SLD}', sld)

filename = "{NNN}_{BRAND}_farm.any".format(BRAND=brand, NNN=nnn)
with open(filename, "w") as outstream:
    outstream.write(data)

answered Dec 1, 2015 at 18:48

mr.zog

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1 Comment

mr.zog Over a year ago

I learned chaining yesterday and string formatting today. I don't know if I should be closing the file but Imet my goal to be able to generate a config file and name it in one fell swoop.

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