005 Packages¶
import¶
Python comes with a good deal of built-in functionality, and that is what we have mainly been using to date. Often though, we need to classes or functions from other packages. Provided these packages are installed in our distribution, we can use them.
The system you should have setup for you includes the packages listed in environment.yml.
When we want to use a non-standard Python package, we must first import it into our codebase. This is done with the import directive, e.g.:
import yaml
to import a library called yaml. We can then access some function XX functions in the package as yaml.XX.
In [1]:
import yaml
help(yaml.safe_load)
Help on function safe_load in module yaml:
safe_load(stream)
Parse the first YAML document in a stream
and produce the corresponding Python object.
Resolve only basic YAML tags. This is known
to be safe for untrusted input.
We will learn in Python Introduction that classes start with a capital letter. So, if we see a variable in Python such aspath`, we should recognise that as a class.
Sometimes we wish to only import certain functions or sub-packages. This is done with the from directive. For example to import the class Path from the package pathlib
In [2]:
from pathlib import Path
The class Path is now available directly as Path, whereas if we had imported it as:
import pathlib
we would have needed to refer to it as pathlib.Path. This will over-ride any current definition of the class Path in the current code, so be careful not to over-ride things you don't mean to.
Exercise 1¶
Make and run a Python cell that imports the class Loader from the package yaml and show the help text for this.
In [3]:
# ANSWER
#
from yaml import Loader
help(Loader)
# This above is a correct answer
# you could have done as below
# but that doesnt quite answer the question correctly
# as it specificaly asks you to import Loader
#
#import yaml
#help(yaml.Loader)
Help on class Loader in module yaml.loader:
class Loader(yaml.reader.Reader, yaml.scanner.Scanner, yaml.parser.Parser, yaml.composer.Composer, yaml.constructor.Constructor, yaml.resolver.Resolver)
| Loader(stream)
|
| Method resolution order:
| Loader
| yaml.reader.Reader
| yaml.scanner.Scanner
| yaml.parser.Parser
| yaml.composer.Composer
| yaml.constructor.Constructor
| yaml.constructor.UnsafeConstructor
| yaml.constructor.FullConstructor
| yaml.constructor.SafeConstructor
| yaml.constructor.BaseConstructor
| yaml.resolver.Resolver
| yaml.resolver.BaseResolver
| builtins.object
|
| Methods defined here:
|
| __init__(self, stream)
| Initialize the scanner.
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.reader.Reader:
|
| check_printable(self, data)
|
| determine_encoding(self)
|
| forward(self, length=1)
|
| get_mark(self)
|
| peek(self, index=0)
|
| prefix(self, length=1)
|
| update(self, length)
|
| update_raw(self, size=4096)
|
| ----------------------------------------------------------------------
| Data descriptors inherited from yaml.reader.Reader:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.reader.Reader:
|
| NON_PRINTABLE = re.compile('[^\t\n\r -~\x85\xa0-\ud7ff\ue000-�𐀀-\U0010...
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.scanner.Scanner:
|
| add_indent(self, column)
|
| check_block_entry(self)
|
| check_directive(self)
|
| check_document_end(self)
|
| check_document_start(self)
|
| check_key(self)
|
| check_plain(self)
|
| check_token(self, *choices)
|
| check_value(self)
|
| fetch_alias(self)
|
| fetch_anchor(self)
|
| fetch_block_entry(self)
|
| fetch_block_scalar(self, style)
|
| fetch_directive(self)
|
| fetch_document_end(self)
|
| fetch_document_indicator(self, TokenClass)
|
| fetch_document_start(self)
|
| fetch_double(self)
|
| fetch_flow_collection_end(self, TokenClass)
|
| fetch_flow_collection_start(self, TokenClass)
|
| fetch_flow_entry(self)
|
| fetch_flow_mapping_end(self)
|
| fetch_flow_mapping_start(self)
|
| fetch_flow_scalar(self, style)
|
| fetch_flow_sequence_end(self)
|
| fetch_flow_sequence_start(self)
|
| fetch_folded(self)
|
| fetch_key(self)
|
| fetch_literal(self)
|
| fetch_more_tokens(self)
|
| fetch_plain(self)
|
| fetch_single(self)
|
| fetch_stream_end(self)
|
| fetch_stream_start(self)
|
| fetch_tag(self)
|
| fetch_value(self)
|
| get_token(self)
|
| need_more_tokens(self)
|
| next_possible_simple_key(self)
|
| peek_token(self)
|
| remove_possible_simple_key(self)
|
| save_possible_simple_key(self)
|
| scan_anchor(self, TokenClass)
|
| scan_block_scalar(self, style)
|
| scan_block_scalar_breaks(self, indent)
|
| scan_block_scalar_ignored_line(self, start_mark)
|
| scan_block_scalar_indentation(self)
|
| scan_block_scalar_indicators(self, start_mark)
|
| scan_directive(self)
|
| scan_directive_ignored_line(self, start_mark)
|
| scan_directive_name(self, start_mark)
|
| scan_flow_scalar(self, style)
|
| scan_flow_scalar_breaks(self, double, start_mark)
|
| scan_flow_scalar_non_spaces(self, double, start_mark)
|
| scan_flow_scalar_spaces(self, double, start_mark)
|
| scan_line_break(self)
|
| scan_plain(self)
|
| scan_plain_spaces(self, indent, start_mark)
|
| scan_tag(self)
|
| scan_tag_directive_handle(self, start_mark)
|
| scan_tag_directive_prefix(self, start_mark)
|
| scan_tag_directive_value(self, start_mark)
|
| scan_tag_handle(self, name, start_mark)
|
| scan_tag_uri(self, name, start_mark)
|
| scan_to_next_token(self)
|
| scan_uri_escapes(self, name, start_mark)
|
| scan_yaml_directive_number(self, start_mark)
|
| scan_yaml_directive_value(self, start_mark)
|
| stale_possible_simple_keys(self)
|
| unwind_indent(self, column)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.scanner.Scanner:
|
| ESCAPE_CODES = {'U': 8, 'u': 4, 'x': 2}
|
| ESCAPE_REPLACEMENTS = {'\t': '\t', ' ': ' ', '"': '"', '/': '/', '0': ...
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.parser.Parser:
|
| check_event(self, *choices)
|
| dispose(self)
|
| get_event(self)
|
| parse_block_mapping_first_key(self)
|
| parse_block_mapping_key(self)
|
| parse_block_mapping_value(self)
|
| parse_block_node(self)
|
| parse_block_node_or_indentless_sequence(self)
|
| parse_block_sequence_entry(self)
|
| parse_block_sequence_first_entry(self)
|
| parse_document_content(self)
|
| parse_document_end(self)
|
| parse_document_start(self)
|
| parse_flow_mapping_empty_value(self)
|
| parse_flow_mapping_first_key(self)
|
| parse_flow_mapping_key(self, first=False)
|
| parse_flow_mapping_value(self)
|
| parse_flow_node(self)
|
| parse_flow_sequence_entry(self, first=False)
|
| parse_flow_sequence_entry_mapping_end(self)
|
| parse_flow_sequence_entry_mapping_key(self)
|
| parse_flow_sequence_entry_mapping_value(self)
|
| parse_flow_sequence_first_entry(self)
|
| parse_implicit_document_start(self)
|
| parse_indentless_sequence_entry(self)
|
| parse_node(self, block=False, indentless_sequence=False)
|
| parse_stream_start(self)
|
| peek_event(self)
|
| process_directives(self)
|
| process_empty_scalar(self, mark)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.parser.Parser:
|
| DEFAULT_TAGS = {'!': '!', '!!': 'tag:yaml.org,2002:'}
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.composer.Composer:
|
| check_node(self)
|
| compose_document(self)
|
| compose_mapping_node(self, anchor)
|
| compose_node(self, parent, index)
|
| compose_scalar_node(self, anchor)
|
| compose_sequence_node(self, anchor)
|
| get_node(self)
|
| get_single_node(self)
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.constructor.UnsafeConstructor:
|
| find_python_module(self, name, mark)
|
| find_python_name(self, name, mark)
|
| make_python_instance(self, suffix, node, args=None, kwds=None, newobj=False)
|
| set_python_instance_state(self, instance, state)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.constructor.UnsafeConstructor:
|
| yaml_multi_constructors = {'tag:yaml.org,2002:python/module:': <functi...
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.constructor.FullConstructor:
|
| construct_python_bytes(self, node)
|
| construct_python_complex(self, node)
|
| construct_python_long(self, node)
|
| construct_python_module(self, suffix, node)
|
| construct_python_name(self, suffix, node)
|
| construct_python_object(self, suffix, node)
|
| construct_python_object_apply(self, suffix, node, newobj=False)
|
| construct_python_object_new(self, suffix, node)
|
| construct_python_str(self, node)
|
| construct_python_tuple(self, node)
|
| construct_python_unicode(self, node)
|
| get_state_keys_blacklist(self)
| # 'extend' is blacklisted because it is used by
| # construct_python_object_apply to add `listitems` to a newly generate
| # python instance
|
| get_state_keys_blacklist_regexp(self)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.constructor.FullConstructor:
|
| yaml_constructors = {'tag:yaml.org,2002:null': <function SafeConstruct...
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.constructor.SafeConstructor:
|
| construct_mapping(self, node, deep=False)
|
| construct_scalar(self, node)
|
| construct_undefined(self, node)
|
| construct_yaml_binary(self, node)
|
| construct_yaml_bool(self, node)
|
| construct_yaml_float(self, node)
|
| construct_yaml_int(self, node)
|
| construct_yaml_map(self, node)
|
| construct_yaml_null(self, node)
|
| construct_yaml_object(self, node, cls)
|
| construct_yaml_omap(self, node)
|
| construct_yaml_pairs(self, node)
|
| construct_yaml_seq(self, node)
|
| construct_yaml_set(self, node)
|
| construct_yaml_str(self, node)
|
| construct_yaml_timestamp(self, node)
|
| flatten_mapping(self, node)
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.constructor.SafeConstructor:
|
| bool_values = {'false': False, 'no': False, 'off': False, 'on': True, ...
|
| inf_value = inf
|
| nan_value = nan
|
| timestamp_regexp = re.compile('^(?P<year>[0-9][0-9][0-9][0-9])\n ......
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.constructor.BaseConstructor:
|
| check_data(self)
|
| check_state_key(self, key)
| Block special attributes/methods from being set in a newly created
| object, to prevent user-controlled methods from being called during
| deserialization
|
| construct_document(self, node)
|
| construct_object(self, node, deep=False)
|
| construct_pairs(self, node, deep=False)
|
| construct_sequence(self, node, deep=False)
|
| get_data(self)
|
| get_single_data(self)
|
| ----------------------------------------------------------------------
| Class methods inherited from yaml.constructor.BaseConstructor:
|
| add_constructor(tag, constructor) from builtins.type
|
| add_multi_constructor(tag_prefix, multi_constructor) from builtins.type
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.resolver.Resolver:
|
| yaml_implicit_resolvers = {'': [('tag:yaml.org,2002:null', re.compile(...
|
| ----------------------------------------------------------------------
| Methods inherited from yaml.resolver.BaseResolver:
|
| ascend_resolver(self)
|
| check_resolver_prefix(self, depth, path, kind, current_node, current_index)
|
| descend_resolver(self, current_node, current_index)
|
| resolve(self, kind, value, implicit)
|
| ----------------------------------------------------------------------
| Class methods inherited from yaml.resolver.BaseResolver:
|
| add_implicit_resolver(tag, regexp, first) from builtins.type
|
| add_path_resolver(tag, path, kind=None) from builtins.type
|
| ----------------------------------------------------------------------
| Data and other attributes inherited from yaml.resolver.BaseResolver:
|
| DEFAULT_MAPPING_TAG = 'tag:yaml.org,2002:map'
|
| DEFAULT_SCALAR_TAG = 'tag:yaml.org,2002:str'
|
| DEFAULT_SEQUENCE_TAG = 'tag:yaml.org,2002:seq'
|
| yaml_path_resolvers = {}
Summary¶
In this section, we have learned how to import packages using import and from.
| command | purpose |
|---|---|
import yaml |
import the package yaml |
from pathlib import Path |
import the method/ class Path from the package pathlib |