I was looking on a web of Python the commands mentioned in title and their difference; however, I have not satisfied with a complete basic understanding of these commands.
Suppose my file has only the following content.
This is the first time I am posing a question on this site, I will appreciate if someone clarifies my doubts for learning the Python. I thank the StackOverflow for this platform.
In the commands read(), readline() and readlines(), one difference is of course reading whole file, or a single line, or specified line.
But I didn't understand the use/necessity of bracket () in these commands. For example, what is the difference in readline() and readline(7)? If the argument 7 exceeds the number of lines in the file, what will be output?
On the web mentioned above, it is explained what the argument in read() does; but it is not mentioned what the argument in readline() or readlines() does?
2 Answers
read(n)
filevar.read()
Reads and returns a string of n characters, or the entire file as a single string if n is not provided.
readline(n)
filevar.readline()
Returns the next line of the file with all text up to and including the newline character. If n is provided as a parameter than only n characters will be returned if the line is longer than n.
readlines(n)
filevar.readlines()
Returns a list of strings, each representing a single line of the file. If n is not provided then all lines of the file are returned. If n is provided then n characters are read but n is rounded up so that an entire line is returned.
For details, you should consult the library documentation, not the tutorial.
From io documentation:
readline(size=-1)Read and return one line from the stream. If
sizeis specified, at mostsizebytes will be read.The line terminator is always
b'\n'for binary files; for text files, the newline argument toopen()can be used to select the line terminator(s) recognized.
readlines(hint=-1)Read and return a list of lines from the stream.
hintcan be specified to control the number of lines read: no more lines will be read if the total size (in bytes/characters) of all lines so far exceedshint.Note that it’s already possible to iterate on file objects using
for line in file: ...without callingfile.readlines().
So, readline() reads an entire line. readline(7) reads at most 7 bytes of a line. readlines() reads all the lines as a list. readlines(7) returns at most 7 lines as a list.
