How to redirect Python’s sys.stdout to StringIO()

Redirect stdout to StringIO()

The following python code will use the capturePrint function to redirect stdio to StringIO() so you can capture info that would normally just be printed. I tested this using the Music21 .show(‘text’) method.


def capturePrint(executableStrThatPrints):

    import sys, StringIO

    # redir sys.stdout
    stdout = sys.stdout
    sys.stdout = reportSIO = StringIO.StringIO()

    reportStr = reportSIO.getvalue()

    # restore sys.stdout so we can print
    sys.stdout = stdout 

    return reportStr

def testCapturePrint():
    from music21 import *
    global sBach
    sBach = corpus.parse('bach/bwv7.7')
    x = capturePrint("""'text')""")
    print x

if __name__ == '__main__':


#music21, #python

Run Ipython magic functions from your profile startup python script

This is the  setup I did for a Music21 project named “chordMe”.

On WIN XP the .ipython configuration dir is in C:Documents and SettingsAdministrator.ipython

Create a profile for your project.

Open a command line shell and type the following to create a new profile

> ipython profile create chordMe
[ProfileCreate] Generating default config file: u'C:Documents and'

Now add the following python file to:
C:Documents and SettingsAdministrator.ipythonprofile_chordMestartup  file content:
# usage:
#     $ ipython --profile=chordMe

import os
from IPython.core.interactiveshell import InteractiveShell 

# from
# run_line_magic(magic_name, line)
# magic_name : str  "Name of the desired magic function, without ‘%’ prefix."
# line : str "The rest of the input line as a single string."

get_ipython().run_line_magic(u"logstart", u"-o append")
from music21 import *

Running Ipython with the startup commands. 
To the command line say:
> ipython --profile=chordMe

#ipython, #music21, #python

Great Comments about my code from MIT’s Music21 creator, Michael Scott Cuthbert

Big thanks to MIT’s Music21 creator, Dr. Michael Scott Cuthbert, for his encouraging comments about my code. It’s nice to know that I am staying current and being of service.

He left comments regarding the code that I published:

On Stack Overflow he said, “…your solution is so elegant that we’ve decided to include some code based on it in spirit in the next release (v1.1) of music21”.

On this blog he said, “Thanks for the great post and ideas! We’ll be incorporating something like this in a music21 midi.realtime module… Please feel free to post this to the music21list (Google Groups). People will be interested!” You can see the Google Group re-post here.

Lastly, let me again express my gratitude to Dr. Cuthbert for his encouragement.

Love and peace,


#music, #music21, #python

How to produce Python controlled audio output from music made with Music21

This post was generated from a question I asked and answered here on Stack Overflow.

# Generates and Plays 2 Music21 Scores "on the fly".
# see way below for source notes

from music21 import *

# we create the music21 Bottom Part, and do this explicitly, one object at a time.

n1 = note.Note('e4')
n1.duration.type = 'whole'
n2 = note.Note('d4')
n2.duration.type = 'whole'
m1 = stream.Measure()
m2 = stream.Measure()
partLower = stream.Part()

# For the music21 Upper Part, we automate the note creation procedure

data1 = [('g4', 'quarter'), ('a4', 'quarter'), ('b4', 'quarter'), ('c#5', 'quarter')]
data2 = [('d5', 'whole')]
data = [data1, data2]
partUpper = stream.Part()

def makeUpperPart(data):
    for mData in data:
        m = stream.Measure()
        for pitchName, durType in mData:
            n = note.Note(pitchName)
            n.duration.type = durType

# Now, we can add both Part objects into a music21 Score object.  

sCadence = stream.Score()
sCadence.insert(0, partUpper)
sCadence.insert(0, partLower)

# Now, let's play the MIDI of the sCadence Score 
# [from memory, ie no file  write necessary] using pygame

import cStringIO

sCadence_mf = sCadence.midiFile
sCadence_mStr = sCadence_mf.writestr()
sCadence_mStrFile = cStringIO.StringIO(sCadence_mStr)

import pygame

freq = 44100    # audio CD quality
bitsize = -16   # unsigned 16 bit
channels = 2    # 1 is mono, 2 is stereo
buffer = 1024    # number of samples
pygame.mixer.init(freq, bitsize, channels, buffer)

# optional volume 0 to 1.0

def play_music(music_file):
    stream music with module in blocking manner
    this will stream the sound from disk while playing
    clock = pygame.time.Clock()
        print "Music file %s loaded!" % music_file
    except pygame.error:
        print "File %s not found! (%s)" % (music_file, pygame.get_error())
        # check if playback has finished

# play the midi file we just saved


# now let's make a new music21 Score by reversing the upperPart notes
data2 = [('d5', 'whole')]
data = [data1, data2]
partUpper = stream.Part()
sCadence2 = stream.Score()
sCadence2.insert(0, partUpper)
sCadence2.insert(0, partLower)

# now let's play the new Score
sCadence2_mf = sCadence2.midiFile
sCadence2_mStr = sCadence2_mf.writestr()
sCadence2_mStrFile = cStringIO.StringIO(sCadence2_mStr)

## There are 3 sources for this mashup:

# 1. Source for the Music21 Score Creation

# 2.  Source for the Music21 MidiFile Class Behaviour

# 3.  Source for the pygame player:

#music21, #python