How do you write to top of file in python?
In modes Show 1st way, can be used if there are no issues to load the file into memory:
2nd way:
I don't know how this method works under the hood and if it can be employed on big big file. The argument 1 passed to input is what allows to rewrite a line in place; the following lines must be moved forwards or backwards in order that the inplace operation takes place, but I don't know the mechanism In this article, we will discuss how to insert single or multiple lines at the beginning of a text or CSV file in python. There is no direct way to insert text in the middle of a file. Therefore we have to create a new file with the new line at the top and then rename this file as the original file. We have created a function for that, import os def prepend_line(file_name, line): """ Insert given string as a new line at the beginning of a file """ # define name of temporary dummy file dummy_file = file_name + '.bak' # open original file in read mode and dummy file in write mode with open(file_name, 'r') as read_obj, open(dummy_file, 'w') as write_obj: # Write given line to the dummy file write_obj.write(line + '\n') # Read lines from original file one by one and append them to the dummy file for line in read_obj: write_obj.write(line) # remove original file os.remove(file_name) # Rename dummy file as the original file os.rename(dummy_file, file_name) What does this function do?
Let’s use this function to insert a line at the beginning of a file. Suppose we have a file ‘sample.txt’ and its contents are, Hello this is a sample file It contains sample text Dummy Line A Dummy Line B Dummy Line C This is the end of file Now add a new line ‘’This is the first line” at the top of the file, # Insert a line before the first line of a file 'sample.txt' prepend_line("sample.txt", "This is a first line") Now the contents of the file are, This is a first line Hello this is a sample file It contains sample text Dummy Line A Dummy Line B Dummy Line C This is the end of file A new line is added at the top of file. Advertisements Insert multiple lines at the top of a fileSuppose we have a list of strings, list_of_lines = ['Another line to prepend', 'Second Line to prepend', 'Third Line to prepend'] We want to add each string in the list as a new line in the file. To insert multiple lines at the beginning of a file, we can call the above created function prepend_line() various times i.e. once for each line like this, [ prepend_line("sample.txt", line) for line in list_of_lines ] But that is not an efficient solution because it will open, close and move contents to a temporary file for each string/line in the list. So, let’s create a function that opens the file only once and also insert multiple lines at the top of file i.e. import os def prepend_multiple_lines(file_name, list_of_lines): """Insert given list of strings as a new lines at the beginning of a file""" # define name of temporary dummy file dummy_file = file_name + '.bak' # open given original file in read mode and dummy file in write mode with open(file_name, 'r') as read_obj, open(dummy_file, 'w') as write_obj: # Iterate over the given list of strings and write them to dummy file as lines for line in list_of_lines: write_obj.write(line + '\n') # Read lines from original file one by one and append them to the dummy file for line in read_obj: write_obj.write(line) # remove original file os.remove(file_name) # Rename dummy file as the original file os.rename(dummy_file, file_name) This function accepts a file name and list of strings as arguments. Then add the strings in the list as newlines in a temporary file and then append the lines from the original file to the temporary file. In the end, rename the temporary file as the original file. Let’s use this function, Contents of the file ‘sample.txt’ are, This is a first line Hello this is a sample file It contains sample text Dummy Line A Dummy Line B Dummy Line C This is the end of file Insert strings in a list as new lines at the top of a file ‘sample.txt’ list_of_lines = ['Another line to prepend', 'Second Line to prepend', 'Third Line to prepend'] # Insert strings in a list as new lines at the top of file 'sample.txt' prepend_multiple_lines("sample.txt", list_of_lines) Now the Contents of the file ‘sample.txt’ are, Another line to prepend Second Line to prepend Third Line to prepend This is a first line Hello this is a sample file It contains sample text Dummy Line A Dummy Line B Dummy Line C This is the end of file The complete example is as follows, import os def prepend_line(file_name, line): """ Insert given string as a new line at the beginning of a file """ # define name of temporary dummy file dummy_file = file_name + '.bak' # open original file in read mode and dummy file in write mode with open(file_name, 'r') as read_obj, open(dummy_file, 'w') as write_obj: # Write given line to the dummy file write_obj.write(line + '\n') # Read lines from original file one by one and append them to the dummy file for line in read_obj: write_obj.write(line) # remove original file os.remove(file_name) # Rename dummy file as the original file os.rename(dummy_file, file_name) def prepend_multiple_lines(file_name, list_of_lines): """Insert given list of strings as a new lines at the beginning of a file""" # define name of temporary dummy file dummy_file = file_name + '.bak' # open given original file in read mode and dummy file in write mode with open(file_name, 'r') as read_obj, open(dummy_file, 'w') as write_obj: # Iterate over the given list of strings and write them to dummy file as lines for line in list_of_lines: write_obj.write(line + '\n') # Read lines from original file one by one and append them to the dummy file for line in read_obj: write_obj.write(line) # remove original file os.remove(file_name) # Rename dummy file as the original file os.rename(dummy_file, file_name) def main(): print('*** Insert a line at the top of a file ***') # Insert a line before the first line of a file 'sample.txt' prepend_line("sample.txt", "This is a first line") print('*** Insert multiple lines at the beginning of a file ***') list_of_lines = ['Another line to prepend', 'Second Line to prepend', 'Third Line to prepend'] # Insert strings in a list as new lines at the top of file 'sample.txt' prepend_multiple_lines("sample.txt", list_of_lines) if __name__ == '__main__': main() How do you append to top of file in Python?Append data to a file as a new line in Python. Open the file in append mode ('a'). Write cursor points to the end of file.. Append '\n' at the end of the file using write() function.. Append the given line to the file using write() function.. Close the file.. How do you write to the first line of a file in Python?Steps for writing to text files
To write to a text file in Python, you follow these steps: First, open the text file for writing (or append) using the open() function. Second, write to the text file using the write() or writelines() method. Third, close the file using the close() method.
How do I put text in a specific position of a file in Python?seek() method
In Python, seek() function is used to change the position of the File Handle to a given specific position. File handle is like a cursor, which defines from where the data has to be read or written in the file.
How do you write over a file in Python?To overwrite a file, to write new content into a file, we have to open our file in “w” mode, which is the write mode. It will delete the existing content from a file first; then, we can write new content and save it. We have a new file with the name “myFile. txt”.
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