Capturing Output With %%capture¶
IPython has a cell magic, %%capture, which captures the stdout/stderr of a cell. With this magic you can discard these streams or store them in a variable.
In [1]:
from __future__ import print_function
import sys
By default, %%capture discards these streams. This is a simple way to suppress unwanted output.
In [2]:
%%capture
print('hi, stdout')
print('hi, stderr', file=sys.stderr)
If you specify a name, then stdout/stderr will be stored in an object in your namespace.
In [3]:
%%capture captured
print('hi, stdout')
print('hi, stderr', file=sys.stderr)
In [4]:
captured
Out[4]:
<IPython.utils.capture.CapturedIO at 0x1076c9310>
Calling the object writes the output to stdout/stderr as appropriate.
In [5]:
captured()
hi, stdout
hi, stderr
In [6]:
captured.stdout
Out[6]:
'hi, stdout\n'
In [7]:
captured.stderr
Out[7]:
'hi, stderr\n'
%%capture grabs all output types, not just stdout/stderr, so you can do plots and use IPython's display system inside %%capture
In [8]:
%matplotlib inline
import matplotlib.pyplot as plt
import numpy as np
In [9]:
%%capture wontshutup
print("setting up X")
x = np.linspace(0,5,1000)
print("step 2: constructing y-data")
y = np.sin(x)
print("step 3: display info about y")
plt.plot(x,y)
print("okay, I'm done now")
In [10]:
wontshutup()
setting up X step 2: constructing y-data step 3: display info about y okay, I'm done now
And you can selectively disable capturing stdout, stderr or rich display, by passing --no-stdout, --no-stderr and --no-display
In [11]:
%%capture cap --no-stderr
print('hi, stdout')
print("hello, stderr", file=sys.stderr)
hello, stderr
In [12]:
cap.stdout
Out[12]:
'hi, stdout\n'
In [13]:
cap.stderr
Out[13]:
''
In [14]:
cap.outputs
Out[14]:
[]