StringIO and BytesIO ​

StringIO ​

Often, data reading and writing do not necessarily involve files; it can also be done in memory.

StringIO, as the name suggests, is used for reading and writing strings (str) in memory.

To write a string to StringIO, we first need to create a StringIO object, and then we can write to it like a file:

from io import StringIO

f = StringIO()
f.write('hello')   # Returns the number of characters written (5)
f.write(' ')       # Returns the number of characters written (1)
f.write('world!')  # Returns the number of characters written (6)
print(f.getvalue())  # 'hello world!'

The getvalue() method is used to obtain the string written to StringIO.

To read from StringIO, we can initialize it with a string and then read from it like reading from a file:

from io import StringIO

f = StringIO('Hello!\nHi!\nGoodbye!')
while True:
    s = f.readline()
    if s == '':
        break
    print(s.strip())

BytesIO ​

StringIO can only handle strings. If you need to work with binary data, you should use BytesIO.

BytesIO allows reading and writing bytes in memory. We create a BytesIO object and write some bytes to it:

from io import BytesIO

f = BytesIO()
f.write('中文'.encode('utf-8'))  # Write UTF-8 encoded bytes
print(f.getvalue())  # Outputs: b'\xe4\xb8\xad\xe6\x96\x87'

Note that what is written is not a string, but rather the bytes encoded in UTF-8.

Similar to StringIO, you can initialize BytesIO with bytes and read from it like reading from a file:

from io import BytesIO

f = BytesIO(b'\xe4\xb8\xad\xe6\x96\x87')
print(f.read())  # Outputs: b'\xe4\xb8\xad\xe6\x96\x87'

Summary ​

StringIO and BytesIO are methods for operating on strings (str) and bytes in memory, respectively, providing a consistent interface similar to reading and writing files.