Rope Overview

The purpose of this file is to give an overview of some of rope's features. It is incomplete. And some of the features shown here are old and do not show what rope can do in extremes. So if you really want to feel the power of rope try its features and see its unit tests.

This file is more suitable for the users. Developers who plan to use rope as a library might find library.txt more useful.

Table of Contents

.ropeproject Folder

Rope uses a folder inside projects for holding project configuration and data. Its default name is .ropeproject, but it can be changed (you can even tell rope not to create this folder).

Currently it is used for things such as:

You can change what to save and what not to in the config.py file.

Refactorings

This section shows some random refactorings that you can perform using rope.

Renaming Attributes

Consider we have:

class AClass(object):

    def __init__(self):
        self.an_attr = 1

    def a_method(self, arg):
        print self.an_attr, arg

a_var = AClass()
a_var.a_method(a_var.an_attr)

After renaming an_attr to new_attr and a_method to new_method we'll have:

class AClass(object):

    def __init__(self):
        self.new_attr = 1

    def new_method(self, arg):
        print self.new_attr, arg

a_var = AClass()
a_var.new_method(a_var.new_attr)

Renaming Function Keyword Parameters

On:

def a_func(a_param):
    print a_param

a_func(a_param=10)
a_func(10)

performing rename refactoring on any occurrence of a_param will result in:

def a_func(new_param):
    print new_param

a_func(new_param=10)
a_func(10)

Renaming modules

Consider the project tree is something like:

root/
  mod1.py
  mod2.py

mod1.py contains:

import mod2
from mod2 import AClass

mod2.a_func()
a_var = AClass()

After performing rename refactoring one of the mod2 occurrences in mod1 we'll get:

import newmod
from newmod import AClass

newmod.a_func()
a_var = AClass()

and the new project tree would be:

root/
  mod1.py
  newmod.py

Renaming Occurrences In Strings And Comments

You can tell rope to rename all occurrences of a name in comments and strings. This can be done by passing docs=True to Rename.get_changes() method. Rope renames names in comments and strings only where the name is visible. For example in:

def f():
    a_var = 1
    # INFO: I'm printing `a_var`
    print 'a_var = %s' % a_var

# f prints a_var

after we rename the a_var local variable in f() to new_var we would get:

def f():
    new_var = 1
    # INFO: I'm printing `new_var`
    print 'new_var = %s' % new_var

# f prints a_var

This makes it safe to assume that this option does not perform wrong renames most of the time.

This also changes occurrences inside evaluated strings:

def func():
    print 'func() called'

eval('func()')

After renaming func to newfunc we should have:

def newfunc():
    print 'newfunc() called'

eval('newfunc()')

Rename When Unsure

This option tells rope to rename when it doesn't know whether it is an exact match or not. For example after renaming C.a_func when the 'rename when unsure' option is set in:

class C(object):

    def a_func(self):
        pass

def a_func(arg):
    arg.a_func()

C().a_func()

we would have:

class C(object):

    def new_func(self):
        pass

def a_func(arg):
    arg.new_func()

C().new_func()

Note that the global a_func was not renamed because we are sure that it is not a match. But when using this option there might be some unexpected renames. So only use this option when the name is almost unique and is not defined in other places.

Move Method Refactoring

It happens when you perform move refactoring on a method of a class. In this refactoring, a method of a class is moved to the class of one of its attributes. The old method will call the new method. If you want to change all of the occurrences of the old method to use the new method you can inline it afterwards.

For instance if you perform move method on a_method in:

class A(object):
    pass

class B(object):

    def __init__(self):
        self.attr = A()

    def a_method(self):
        pass

b = B()
b.a_method()

You will be asked for the destination field and the name of the new method. If you use attr and new_method in these fields and press enter, you'll have:

class A(object):

    def new_method(self):
        pass

class B(object):

    def __init__(self):
        self.attr = A()

    def a_method(self):
        return self.attr.new_method()


b = B()
b.a_method()

Now if you want to change the occurrences of B.a_method() to use A.new_method(), you can inline B.a_method():

class A(object):

    def new_method(self):
        pass

class B(object):

    def __init__(self):
        self.attr = A()

b = B()
b.attr.new_method()

Moving Fields

Rope does not have a separate refactoring for moving fields. Rope's refactorings are very flexible, though. You can use the rename refactoring to move fields. For instance:

class A(object):
    pass

class B(object):

    def __init__(self):
        self.a = A()
        self.attr = 1

b = B()
print(b.attr)

consider we want to move attr to A. We can do that by renaming attr to a.attr:

class A(object):
    pass

class B(object):

    def __init__(self):
        self.a = A()
        self.a.attr = 1

b = B()
print(b.a.attr)

You can move the definition of attr manually.

Extract Method

In these examples ${region_start} and ${region_end} show the selected region for extraction:

def a_func():
    a = 1
    b = 2 * a
    c = ${region_start}a * 2 + b * 3${region_end}

After performing extract method we'll have:

def a_func():
    a = 1
    b = 2 * a
    c = new_func(a, b)

def new_func(a, b):
    return a * 2 + b * 3

For multi-line extractions if we have:

def a_func():
    a = 1
    ${region_start}b = 2 * a
    c = a * 2 + b * 3${region_end}
    print b, c

After performing extract method we'll have:

def a_func():
    a = 1
    b, c = new_func(a)
    print b, c

def new_func(a):
    b = 2 * a
    c = a * 2 + b * 3
    return b, c

Extracting Similar Expressions/Statements

When performing extract method or local variable refactorings you can tell rope to extract similar expressions/statements. For instance in:

if True:
    x = 2 * 3
else:
    x = 2 * 3 + 1

Extracting 2 * 3 will result in:

six = 2 * 3
if True:
    x = six
else:
    x = six + 1

Extract Method In staticmethods/classmethods

The extract method refactoring has been enhanced to handle static and class methods better. For instance in:

class A(object):

    @staticmethod
    def f(a):
        b = a * 2

if you extract a * 2 as a method you'll get:

class A(object):

    @staticmethod
    def f(a):
        b = A.twice(a)

    @staticmethod
    def twice(a):
        return a * 2

Inline Method Refactoring

Inline method refactoring can add imports when necessary. For instance consider mod1.py is:

import sys


class C(object):
    pass

def do_something():
    print sys.version
    return C()

and mod2.py is:

import mod1


c = mod1.do_something()

After inlining do_something, mod2.py would be:

import mod1
import sys


print sys.version
c = mod1.C()

Rope can inline methods, too:

class C(object):

    var = 1

    def f(self, p):
        result = self.var + pn
        return result


c = C()
x = c.f(1)

After inlining C.f(), we'll have:

class C(object):

    var = 1

c = C()
result = c.var + pn
x = result

As another example we will inline a classmethod:

class C(object):
    @classmethod
    def say_hello(cls, name):
        return 'Saying hello to %s from %s' % (name, cls.__name__)
hello = C.say_hello('Rope')

Inlining say_hello will result in:

class C(object):
    pass
hello = 'Saying hello to %s from %s' % ('Rope', C.__name__)

Inlining Parameters

rope.refactor.inline.create_inline() creates an InlineParameter object when performed on a parameter. It passes the default value of the parameter wherever its function is called without passing it. For instance in:

def f(p1=1, p2=1):
    pass

f(3)
f()
f(3, 4)

after inlining p2 parameter will have:

def f(p1=1, p2=1):
    pass

f(3, 2)
f(p2=2)
f(3, 4)

Use Function Refactoring

It tries to find the places in which a function can be used and changes the code to call it instead. For instance if mod1 is:

def square(p):
    return p ** 2

my_var = 3 ** 2

and mod2 is:

another_var = 4 ** 2

if we perform "use function" on square function, mod1 will be:

def square(p):
    return p ** 2

my_var = square(3)

and mod2 will be:

import mod1
another_var = mod1.square(4)

Automatic Default Insertion In Change Signature

The rope.refactor.change_signature.ArgumentReorderer signature changer takes a parameter called autodef. If not None, its value is used whenever rope needs to insert a default for a parameter (that happens when an argument without default is moved after another that has a default value). For instance in:

def f(p1, p2=2):
    pass

if we reorder using:

changers = [ArgumentReorderer([1, 0], autodef='1')]

will result in:

def f(p2=2, p1=1):
    pass

Sorting Imports

Organize imports sorts imports, too. It does that according to PEP 8:

[__future__ imports]

[standard imports]

[third-party imports]

[project imports]


[the rest of module]

Handling Long Imports

Handle long imports command trys to make long imports look better by transforming import pkg1.pkg2.pkg3.pkg4.mod1 to from pkg1.pkg2.pkg3.pkg4 import mod1. Long imports can be identified either by having lots of dots or being very long. The default configuration considers imported modules with more than 2 dots or with more than 27 characters to be long.

Stoppable Refactorings

Some refactorings might take a long time to finish (based on the size of your project). The get_changes() method of these refactorings take a parameter called task_handle. If you want to monitor or stop these refactoring you can pass a rope.refactor. taskhandle.TaskHandle to this method. See rope.refactor.taskhandle module for more information.

Basic Implicit Interfaces

Implicit interfaces are the interfaces that you don't explicitly define; But you expect a group of classes to have some common attributes. These interfaces are very common in dynamic languages; Since we only have implementation inheritance and not interface inheritance. For instance:

class A(object):

    def count(self):
        pass

class B(object):

    def count(self):
        pass

def count_for(arg):
    return arg.count()

count_for(A())
count_for(B())

Here we know that there is an implicit interface defined by the function count_for that provides count(). Here when we rename A.count() we expect B.count() to be renamed, too. Currently rope supports a basic form of implicit interfaces. When you try to rename an attribute of a parameter, rope renames that attribute for all objects that have been passed to that function in different call sites. That is renaming the occurrence of count in count_for function to newcount will result in:

class A(object):

    def newcount(self):
        pass

class B(object):

    def newcount(self):
        pass

def count_for(arg):
    return arg.newcount()

count_for(A())
count_for(B())

This also works for change method signature. Note that this feature relies on rope's object analysis mechanisms to find out the parameters that are passed to a function.

Restructurings

rope.refactor.restructure can be used for performing restructurings. A restructuring is a program transformation; not as well defined as other refactorings like rename. In this section, we'll see some examples. After this example you might like to have a look at:

  • rope.refactor.restructure for more examples and features not described here like adding imports to changed modules.
  • rope.refactor.wildcards for an overview of the arguments the default wildcard supports.

Finally, restructurings can be improved in many ways (for instance adding new wildcards). You might like to discuss your ideas in the mailing list.

Example 1

In its basic form we have a pattern and a goal. Consider we were not aware of the ** operator and wrote our own

def pow(x, y):
    result = 1
    for i in range(y):
        result *= x
    return result

print pow(2, 3)

Now that we know ** exists we want to use it wherever pow is used (there might be hundreds of them!). We can use a pattern like:

pattern: pow(${param1}, ${param2})

Goal can be something like:

goal: ${param1} ** ${param2}

Note that ${...} can be used to match expressions. By default every expression at that point will match.

You can use the matched names in goal and they will be replaced with the string that was matched in each occurrence. So the outcome of our restructuring will be:

def pow(x, y):
    result = 1
    for i in range(y):
        result *= x
    return result

print 2 ** 3

It seems to be working but what if pow is imported in some module or we have some other function defined in some other module that uses the same name and we don't want to change it. Wildcard arguments come to rescue. Wildcard arguments is a mapping; Its keys are wildcard names that appear in the pattern (the names inside ${...}).

The values are the parameters that are passed to wildcard matchers. The arguments a wildcard takes is based on its type.

For checking the type of a wildcard, we can pass type=value as an argument; value should be resolved to a python variable (or reference). For instance for specifying pow in this example we can use mod.pow. As you see, this string should start from module name. For referencing python builtin types and functions you can use __builtin__ module (for instance __builtin__.int).

For solving the mentioned problem, we change our pattern. But goal remains the same:

pattern: ${pow_func}(${param1}, ${param2})
goal: ${param1} ** ${param2}

Consider the name of the module containing our pow function is mod. args can be:

pow_func: name=mod.pow

If we need to pass more arguments to a wildcard matcher we can use , to separate them. Such as name: type=mod.MyClass,exact.

This restructuring handles aliases; like in:

mypow = pow
result = mypow(2, 3)

Transforms into:

mypow = pow
result = 2 ** 3

If we want to ignore aliases we can pass exact as another wildcard argument:

pattern: ${pow}(${param1}, ${param2})
goal: ${param1} ** ${param2}
args: pow: name=mod.pow, exact

${name}, by default, matches every expression at that point; if exact argument is passed to a wildcard only the specified name will match (for instance, if exact is specified , ${name} matches name and x.name but not var nor (1 + 2) while a normal ${name} can match all of them).

For performing this refactoring using rope library see library.txt.

Example 2

As another example consider:

class A(object):

    def f(self, p1, p2):
        print p1
        print p2


a = A()
a.f(1, 2)

Later we decide that A.f() is doing too much and we want to divide it to A.f1() and A.f2():

class A(object):

    def f(self, p1, p2):
        print p1
        print p2

    def f1(self, p):
        print p

    def f2(self, p):
        print p


a = A()
a.f(1, 2)

But who's going to fix all those nasty occurrences (actually this situation can be handled using inline method refactoring but this is just an example; consider inline refactoring is not implemented yet!). Restructurings come to rescue:

pattern: ${inst}.f(${p1}, ${p2})
goal:
 ${inst}.f1(${p1})
 ${inst}.f2(${p2})

args:
 inst: type=mod.A

After performing we will have:

class A(object):

    def f(self, p1, p2):
        print p1
        print p2

    def f1(self, p):
        print p

    def f2(self, p):
        print p


a = A()
a.f1(1)
a.f2(2)

Example 3

If you like to replace every occurrences of x.set(y) with x = y when x is an instance of mod.A in:

from mod import A

a = A()
b = A()
a.set(b)

We can perform a restructuring with these information:

pattern: ${x}.set(${y})
goal: ${x} = ${y}

args: x: type=mod.A

After performing the above restructuring we'll have:

from mod import A

a = A()
b = A()
a = b

Note that mod.py contains something like:

class A(object):

    def set(self, arg):
        pass

Issues

Pattern names can appear only at the start of an expression. For instance var.${name} is invalid. These situations can usually be fixed by specifying good checks, for example on the type of var and using a ${var}.name.

Object Inference

This section is a bit out of date. Static object inference can do more than described here (see unittests). Hope to update this someday!

Static Object Inference

class AClass(object):

    def __init__(self):
        self.an_attr = 1

    def call_a_func(self):
        return a_func()

def a_func():
    return AClass()

a_var = a_func()
#a_var.${codeassist}

another_var = a_var
#another_var.${codeassist}
#another_var.call_a_func().${codeassist}

Basic support for builtin types:

a_list = [AClass(), AClass()]
for x in a_list:
    pass
    #x.${codeassist}
#a_list.pop().${codeassist}

a_dict = ['text': AClass()]
for key, value in a_dict.items():
    pass
    #key.${codeassist}
    #value.${codeassist}

Enhanced static returned object inference:

class C(object):

    def c_func(self):
        return ['']

def a_func(arg):
    return arg.c_func()

a_var = a_func(C())

Here rope knows that the type of a_var is a list that holds strs.

Supporting generator functions:

class C(object):
    pass

def a_generator():
    yield C()


for c in a_generator():
    a_var = c

Here the objects a_var and c hold are known.

Rope collects different types of data during SOA, like per name data for builtin container types:

l1 = [C()]
var1 = l1.pop()

l2 = []
l2.append(C())
var2 = l2.pop()

Here rope can easily infer the type of var1. But for knowing the type of var2, it needs to analyze the items inserted into l2 which might happen in other modules. Rope can do that by running SOA on that module.

You might be wondering is there any reason for using DOA instead of SOA. The answer is that DOA might be more accurate and handles complex and dynamic situations. For example in:

def f(arg):
    return eval(arg)

a_var = f('C')

SOA can no way conclude the object a_var holds but it is really trivial for DOA. What's more SOA only analyzes calls in one module while DOA analyzes any call that happens when running a module. That is, for achieving the same result as DOA you might need to run SOA on more than one module and more than once (not considering dynamic situations.) One advantage of SOA is that it is much faster than DOA.

Dynamic Object Analysis

PyCore.run_module() runs a module and collects object information if perform_doa project config is set. Since as the program runs rope gathers type information, the program runs much slower. After the program is run, you can get better code assists and some of the refactorings perform much better.

mod1.py:

def f1(param):
    pass
    #param.${codeassist}
    #f2(param).${codeassist}

def f2(param):
    #param.${codeassist}
    return param

Using code assist in specified places does not give any information and there is actually no information about the return type of f2 or param parameter of f1.

mod2.py:

import mod1

class A(object):

    def a_method(self):
        pass

a_var = A()
mod1.f1(a_var)

Retry those code assists after performing DOA on mod2 module.

Builtin Container Types

Builtin types can be handled in a limited way, too:

class A(object):

    def a_method(self):
        pass

def f1():
    result = []
    result.append(A())
    return result

returned = f()
#returned[0].${codeassist}

Test the the proposed completions after running this module.

Guessing Function Returned Value Based On Parameters

mod1.py:

class C1(object):

    def c1_func(self):
        pass

class C2(object):

    def c2_func(self):
        pass


def func(arg):
    if isinstance(arg, C1):
        return C2()
    else:
        return C1()

func(C1())
func(C2())

After running mod1 either SOA or DOA on this module you can test:

mod2.py:

import mod1

arg = mod1.C1()
a_var = mod1.func(arg)
a_var.${codeassist}
mod1.func(mod1.C2()).${codeassist}

Automatic SOA

When turned on, it analyzes the changed scopes of a file when saving for obtaining object information; So this might make saving files a bit more time consuming. By default, this feature is turned on, but you can turn it off by editing your project config.py file, though that is not recommended.

Validating Object DB

Since files on disk change over time project objectdb might hold invalid information. Currently there is a basic incremental objectdb validation that can be used to remove or fix out of date information. Rope uses this feature by default but you can disable it by editing config.py.

Custom Source Folders

By default rope searches the project for finding source folders (folders that should be searched for finding modules). You can add paths to that list using source_folders project config. Note that rope guesses project source folders correctly most of the time. You can also extend python path using python_path config.

Version Control Systems Support

When you perform refactorings some files might need to be moved (when renaming a module) or new files might be created. When you use a VCS rope uses that to perform file system actions.

Currently rope supports Subversion (Uses pysvn library) and Mercurial. Rope uses Subversion if the pysvn module is available and there is a .svn in project root. The Mercurial will be used if mercurial module is available and there is a .hg in project root. Rope assumes either all files are under version control in a project or there is no version control at all. Also don't forget to commit your changes yourself, rope doesn't do that.

Adding support for other VCSs is easy; have a look at library.txt.