Alternative File Reading Methods¶
Once you have a file “object”, the thing returned by the open function, Python provides three methods to read data
from that object. The read() method returns the entire contents of the file as a single string (or just some characters if you provide a number as an input parameter.
The readlines method returns the entire contents of
the entire file as a list of strings, where each item in the list is
one line of the file. The readline method reads one line from the file and
returns it as a string. The strings returned by readlines or readline will contain the
newline character at the end. Table 2 summarizes these methods
and the following session shows them in action.
| Method Name | Use | Explanation |
|---|---|---|
write |
filevar.write(astring) |
Add astring to the end of the file. filevar must refer to a file that has been opened for writing. |
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. |
In this course, we will generally either iterate through the lines returned by readlines() with a for loop, or use read() to get all of the contents as a single string.
In other programming languages, where they don’t have the convenient for loop method of going through the lines of the file one by one, they use a different pattern which requires a different kind of loop,
the while loop. Fortunately, you don’t need to learn this other pattern, and we will put off consideration of while loops until later in this course. We don’t need them for handling data from files.
Note
A common error that novice programmers make is not realizing that all these ways of reading the file contents, use up the file. After you call readlines(), if you call it again you’ll get an empty list.