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environment.py
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environment.py
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import os
import os.path
import collections
import inspect
class NameModifier(object):
def __init__(self, name, **kwargs):
self.name = name
self.args = {'name': name}
self.args.update(kwargs)
class NameValueModifier(object):
def __init__(self, name, value, **kwargs):
self.name = name
self.value = value
self.args = {'name': name, 'value': value}
self.args.update(kwargs)
class SetEnv(NameValueModifier):
def execute(self):
os.environ[self.name] = str(self.value)
class UnsetEnv(NameModifier):
def execute(self):
os.environ.pop(self.name, None) # Avoid throwing if the variable was not set
class SetPath(NameValueModifier):
def execute(self):
string_path = concatenate_paths(self.value)
os.environ[self.name] = string_path
class AppendPath(NameValueModifier):
def execute(self):
environment_value = os.environ.get(self.name, '')
directories = environment_value.split(':') if environment_value else []
directories.append(os.path.normpath(self.value))
os.environ[self.name] = ':'.join(directories)
class PrependPath(NameValueModifier):
def execute(self):
environment_value = os.environ.get(self.name, '')
directories = environment_value.split(':') if environment_value else []
directories = [os.path.normpath(self.value)] + directories
os.environ[self.name] = ':'.join(directories)
class RemovePath(NameValueModifier):
def execute(self):
environment_value = os.environ.get(self.name, '')
directories = environment_value.split(':') if environment_value else []
directories = [os.path.normpath(x) for x in directories if x != os.path.normpath(self.value)]
os.environ[self.name] = ':'.join(directories)
class EnvironmentModifications(object):
"""
Keeps track of requests to modify the current environment.
Each call to a method to modify the environment stores the extra information on the caller in the request:
- 'filename' : filename of the module where the caller is defined
- 'lineno': line number where the request occurred
- 'context' : line of code that issued the request that failed
"""
def __init__(self, other=None):
"""
Initializes a new instance, copying commands from other if it is not None
Args:
other: another instance of EnvironmentModifications from which (optional)
"""
self.env_modifications = []
if other is not None:
self.extend(other)
def __iter__(self):
return iter(self.env_modifications)
def __len__(self):
return len(self.env_modifications)
def extend(self, other):
self._check_other(other)
self.env_modifications.extend(other.env_modifications)
@staticmethod
def _check_other(other):
if not isinstance(other, EnvironmentModifications):
raise TypeError('other must be an instance of EnvironmentModifications')
def _get_outside_caller_attributes(self):
stack = inspect.stack()
try:
_, filename, lineno, _, context, index = stack[2]
context = context[index].strip()
except Exception:
filename, lineno, context = 'unknown file', 'unknown line', 'unknown context'
args = {
'filename': filename,
'lineno': lineno,
'context': context
}
return args
def set(self, name, value, **kwargs):
"""
Stores in the current object a request to set an environment variable
Args:
name: name of the environment variable to be set
value: value of the environment variable
"""
kwargs.update(self._get_outside_caller_attributes())
item = SetEnv(name, value, **kwargs)
self.env_modifications.append(item)
def unset(self, name, **kwargs):
"""
Stores in the current object a request to unset an environment variable
Args:
name: name of the environment variable to be set
"""
kwargs.update(self._get_outside_caller_attributes())
item = UnsetEnv(name, **kwargs)
self.env_modifications.append(item)
def set_path(self, name, elts, **kwargs):
"""
Stores a request to set a path generated from a list.
Args:
name: name o the environment variable to be set.
elts: elements of the path to set.
"""
kwargs.update(self._get_outside_caller_attributes())
item = SetPath(name, elts, **kwargs)
self.env_modifications.append(item)
def append_path(self, name, path, **kwargs):
"""
Stores in the current object a request to append a path to a path list
Args:
name: name of the path list in the environment
path: path to be appended
"""
kwargs.update(self._get_outside_caller_attributes())
item = AppendPath(name, path, **kwargs)
self.env_modifications.append(item)
def prepend_path(self, name, path, **kwargs):
"""
Same as `append_path`, but the path is pre-pended
Args:
name: name of the path list in the environment
path: path to be pre-pended
"""
kwargs.update(self._get_outside_caller_attributes())
item = PrependPath(name, path, **kwargs)
self.env_modifications.append(item)
def remove_path(self, name, path, **kwargs):
"""
Stores in the current object a request to remove a path from a path list
Args:
name: name of the path list in the environment
path: path to be removed
"""
kwargs.update(self._get_outside_caller_attributes())
item = RemovePath(name, path, **kwargs)
self.env_modifications.append(item)
def group_by_name(self):
"""
Returns a dict of the modifications grouped by variable name
Returns:
dict mapping the environment variable name to the modifications to be done on it
"""
modifications = collections.defaultdict(list)
for item in self:
modifications[item.name].append(item)
return modifications
def clear(self):
"""
Clears the current list of modifications
"""
self.env_modifications.clear()
def apply_modifications(self):
"""
Applies the modifications and clears the list
"""
modifications = self.group_by_name()
# Apply the modifications to the environment variables one variable at a time
for name, actions in sorted(modifications.items()):
for x in actions:
x.execute()
def concatenate_paths(paths):
"""
Concatenates an iterable of paths into a string of column separated paths
Args:
paths: iterable of paths
Returns:
string
"""
return ':'.join(str(item) for item in paths)
def set_or_unset_not_first(variable, changes, errstream):
"""
Check if we are going to set or unset something after other modifications have already been requested
"""
indexes = [ii for ii, item in enumerate(changes) if ii != 0 and type(item) in [SetEnv, UnsetEnv]]
if indexes:
good = '\t \t{context} at {filename}:{lineno}'
nogood = '\t--->\t{context} at {filename}:{lineno}'
errstream('Suspicious requests to set or unset the variable \'{var}\' found'.format(var=variable))
for ii, item in enumerate(changes):
print_format = nogood if ii in indexes else good
errstream(print_format.format(**item.args))
def validate(env, errstream):
"""
Validates the environment modifications to check for the presence of suspicious patterns. Prompts a warning for
everything that was found
Current checks:
- set or unset variables after other changes on the same variable
Args:
env: list of environment modifications
"""
modifications = env.group_by_name()
for variable, list_of_changes in sorted(modifications.items()):
set_or_unset_not_first(variable, list_of_changes, errstream)