python - How to open a file and change a line -

i've looked @ loads of threads on cant find right answer:

i'm bit new python. im opening file in python, inserting 1 line before beginning line , 1 before last line , reconstructing lines string variable @ end.

heres function im trying run on opened file. changes lines mode="0" mode="1" or vice versa.

def modes(file, mode):     endstring = ''     if(mode == 1):         mode0 = 'mode="0"'         mode1 = 'mode="1"'     else:         mode0 = 'mode="1"'         mode1 = 'mode="0"'        line in iter(file):         if 'modes' in line:             line = line.replace(mode0,mode1)         endstring += line     return endstring 

so try following:

  mode = 1   input_file = open("c:\myfile.txt")   input_file.readlines()   lengthlines = len(input_file)   #insert line @ position 1   input_file.insert(1,'<variable name="init1" />')   #insert line @ last line position - 1   input_file.insert(lengthlines,'<variable name="init2" />')   #join lines again   input_file = "".join(input_file)   #run modes function - replace occurrences of mode=x   finalfile = modes(input_file,mode)   print finalfile 

and im getting error, "object of type file, has no "len()"" , general object/list errors.

it seems im getting objects/lists etc mixed im not sure - grateful assistance - cheers

input_file.readlines() returns content not assign input_file. you'll have assign return value of call variable, so:

file_content = input_file.readlines() 

and pass len()

lengthlines = len(file_content) 

edit: solving issue len() leads further exceptions. should want:

mode = 1 open("c:\myfile.txt") input_file:     file_content = list(input_file.readlines()) file_content.insert(0,'<variable name="init1" />') file_content.append('<variable name="init2" />') finalfile = modes(file_content,mode) print finalfile 

you might have alter string concatenation in function if want stick several lines.

    endstring += line + '\n' return endstring.rstrip('\n') 

this not yet write new content file though.

edit2: , practice close file when done it, therefore updated above use context manager takes care of this. explicitly call input_file.close() after finished.