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Pyflyby is a set of Python programming productivity tools for Python 2.7 and 3.7+.

For command-line interaction:
  • py: command-line multitool
For IPython interaction:
  • autoimporter: automatically imports symbols when needed.
For editing python source code:
  • tidy-imports: adds missing 'import's, removes unused 'import's, and also reformats import blocks.
  • find-import: prints to stdout how to import a particular symbol.
  • reformat-imports: reformats import blocks
  • collect-imports: prints out all the imports in a given set of files.
  • collect-exports: prints out definitions in a given set of modules, in the form of import statements.
  • transform-imports: renames imported modules/functions.


$ pip install pyflyby
This creates an alias for your ipython named py which runs the pyflyby plug internally.
pyflyby has a dependency on ipython, if it isn't already installed do install it with:
$ pip install ipython

Quick start: Autoimporter + IPython

$ py
In [1]:"[a-z]+", "....hello...").group(0)
[PYFLYBY] import re
Out[1]: 'hello'

In [2]: chisqprob(arange(5), 2)
[PYFLYBY] from numpy import arange
[PYFLYBY] from scipy.stats import chisqprob
Out[2]: [ 1.      0.6065  0.3679  0.2231  0.1353]

To load pyflyby into an existing IPython session as a 1-off:

$ ipython
In [1]: %load_ext pyflyby

To configure IPython/Jupyter Notebook to load pyflyby automatically:

$ py pyflyby.install_in_ipython_config_file


$ echo 'c.InteractiveShellApp.extensions.append("pyflyby")' \
  >> ~/.ipython/profile_default/

$ ipython
In [1]: b64decode('aGVsbG8=')
[PYFLYBY] from base64 import b64decode
Out[1]: 'hello'

Quick start: py command-line multi-tool

$ py b64decode aGVsbG8=
[PYFLYBY] from base64 import b64decode
[PYFLYBY] b64decode('aGVsbG8=', altchars=None)

$ py log2 sys.maxint
[PYFLYBY] from numpy import log2
[PYFLYBY] import sys
[PYFLYBY] log2(9223372036854775807)

$ py 'plot(cos(arange(30)))'
[PYFLYBY] from numpy import arange
[PYFLYBY] from numpy import cos
[PYFLYBY] from matplotlib.pyplot import plot
[PYFLYBY] plot(cos(arange(30)))

$ py 38497631 / 13951446

$ py

Quick start: tidy-imports

To use tidy-imports, just specify the filename(s) to tidy.

For example:

$ echo '"[a-z]+", "....hello..."), chisqprob(arange(5), 2)' >

$ tidy-imports
--- /tmp/
+++ /tmp/
@@ -1 +1,9 @@
+from __future__ import absolute_import, division, with_statement
+from   numpy                    import arange
+from   scipy.stats              import chisqprob
+import re
+"[a-z]+", "....hello..."), chisqprob(arange(5), 2)

Replace /tmp/ [y/N]

Quick start: import libraries

Create a file named .pyflyby with lines such as

from mypackage.mymodule import MyClass, my_function
import anotherpackage.anothermodule

You can put this file in your home directory or in the same directory as your *.py files.

Details: automatic imports

AUTOMATIC IMPORTS - never type "import" again!

This module allows your "known imports" to work automatically in your IPython interactive session without having to type the 'import' statements (and also without having to slow down your Python startup with imports you only use occasionally).


In [1]:"[a-z]+", "....hello...").group(0)
[PYFLYBY] import re
Out[1]: 'hello'

In [2]: chisqprob(arange(5), 2)
[PYFLYBY] from numpy import arange
[PYFLYBY] from scipy.stats import chisqprob
Out[2]: [ 1.      0.6065  0.3679  0.2231  0.1353]

In [3]: np.sin(arandom(5))
[PYFLYBY] from numpy.random import random as arandom
[PYFLYBY] import numpy as np
Out[3]: [ 0.0282  0.0603  0.4653  0.8371  0.3347]

In [4]: isinstance(42, Number)
[PYFLYBY] from numbers import Number
Out[4]: True

It just works

Tab completion works, even on modules that are not yet imported. In the following example, notice that numpy is imported when we need to know its members, and only then:

$ ipython
In [1]: nump<TAB>
In [1]: numpy
In [1]: numpy.arang<TAB>
[PYFLYBY] import numpy
In [1]: numpy.arange

The IPython "?" magic help (pinfo/pinfo2) automatically imports symbols first if necessary:

$ ipython
In [1]: arange?
[PYFLYBY] from numpy import arange
... Docstring: arange([start,] stop[, step,], dtype=None) ...

Other IPython magic commands work as well:

$ ipython
In [1]: %timeit np.cos(pi)
[PYFLYBY] import numpy as np
[PYFLYBY] from numpy import pi
100000 loops, best of 3: 2.51 us per loop

$ echo 'print arange(4)' >
$ ipython
In [1]: %run
[PYFLYBY] from numpy import arange
[0 1 2 3]

Implementation details

The automatic importing happens at parse time, before code is executed. The namespace never contains entries for names that are not yet imported.

This method of importing at parse time contrasts with previous implementations of automatic importing that use proxy objects. Those implementations using proxy objects don't work as well, because it is impossible to make proxy objects behave perfectly. For example, instance(x, T) will return the wrong answer if either x or T is a proxy object.


Tested with:
  • Python 2.6, 2.7, 3.7, 3.8
  • IPython 0.10, 0.11, 0.12, 0.13, 1.0, 1.2, 2.0, 2.1, 2.2, 2.3, 2.4, 3.0, 3.1, 3.2, 4.0., 7.11 (latest)
  • IPython (text console), IPython Notebook, Spyder

Details: import libraries

Pyflyby uses "import libraries" that tell how to import a given symbol.

An import library file is simply a python source file containing 'import' (or 'from ... import ...') lines. These can be generated automatically with collect-imports and collect-exports.

Known imports

Find-imports, tidy-imports, and autoimport consult the database of known imports to figure out where to get an import. For example, if the imports database contains:

from numpy import arange, NaN

then when you type the following in IPython:


the autoimporter would automatically execute from numpy import arange.

The database can be one file or multiple files. This makes it easy to have project-specific known_imports along with global and per-user defaults.

The PYFLYBY_PATH environment variable specifies which files to read. This is a colon-separated list of filenames or directory names. The default is:


If you set:


then this replaces the default.

You can use a hyphen to include the default in the path. If you set:


then this reads /foo1/bar1, then the default locations, then /foo2/bar2.

In $PYFLYBY_PATH, .../.pyflyby (with _three_ dots) means that all ancestor directories are searched for a member named ".pyflyby".

For example, suppose the following files exist:


Further, suppose:

  • /proj is on a separate file system from /.
  • $HOME=/u/quarl

Then tidy-imports /proj/share/mypythonstuff/foo/bar/quux/ will by default use the following:

/proj/share/mypythonstuff/.pyflyby (a file)


  • /.pyflyby is not included, because traversal stops at file system boundaries, and in this example, /proj is on a different file system than /.
  • .pyflyby (in $HOME or near the target file) can be a file or a directory. If it is a directory, then it is recursively searched for *.py files.
  • The order usually doesn't matter, but if there are "forget" instructions (see below), then the order matters. In the default $PYFLYBY_PATH, .../.pyflyby is placed last so that per-directory configuration can override per-user configuration, which can override systemwide configuration.

Forgetting imports

Occasionally you may have reason to tell pyflyby to "forget" entries from the database of known imports.

You can put the following in any file reachable from $PYFLYBY_PATH:

__forget_imports__ = ["from numpy import NaN"]

This is useful if you want to use a set of imports maintained by someone else except for a few particular imports.

Entries in $PYFLYBY_PATH are processed left-to-right in the order specified, so put the files containing these at the end of your $PYFLYBY_PATH. By default, tidy-imports and friends process /etc/pyflyby, then ~/.pyflyby, then the per-directory .pyflyby.

Mandatory imports

Within a certain project you may have a policy to always include certain imports. For example, maybe you always want to do from __future__ import division in all files.

You can put the following in any file reachable from $PYFLYBY_PATH:

__mandatory_imports__ = ["from __future__ import division"]

To undo mandatory imports inherited from other .pyflyby files, use __forget_imports__ (see above).

Canonicalize imports

Sometimes you want every run of tidy-imports to automatically rename an import to a new name.

You can put the following in any file reachable from $PYFLYBY_PATH:

__canonical_imports__ = {"oldmodule.oldfunction": "newmodule.newfunction"}

This is equivalent to running:

tidy-imports --transform=oldmodule.oldfunction=newmodule.newfunction

Soapbox: avoid "star" imports

When programming in Python, a good software engineering practice is to avoid using from foopackage import * in production code.

This style is a maintenance nightmare:

  • It becomes difficult to figure out where various symbols (functions/classes/etc) come from.
  • It's hard to tell what gets shadowed by what.
  • When the package changes in trivial ways, your code will be affected. Consider the following example: Suppose contains import sys, and contains from foopackage import *; if some_condition: sys.exit(0). If changes so that import sys is removed, is now broken because it's missing import sys.

To fix such code, you can run tidy-imports --replace-star-imports to automatically replace star imports with the specific needed imports.

Emacs support

  • To get a M-x tidy-imports command in GNU Emacs, add to your ~/.emacs:

    (load "/path/to/pyflyby/lib/emacs/pyflyby.el")
  • Pyflyby.el doesn't yet work with XEmacs; patches welcome.


This plugin was contributed back to the community by the D. E. Shaw group.

Pyflyby is written by Karl Chen <>


Pyflyby is released under a very permissive license, the MIT/X11 license; see LICENSE.txt.