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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
>
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32.2. ast — 抽象構文木 — Python 3.6.5 ドキュメント
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)
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var
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class
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id
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>
</
span
>
<
h1
>
32.2.
<
a
class
="
reference internal
"
href
="
#module-ast
"
title
="
ast: Abstract Syntax Tree classes and manipulation.
"
>
<
code
class
="
xref py py-mod docutils literal
"
>
<
span
class
="
pre
"
>
ast
</
span
>
</
code
>
</
a
>
— 抽象構文木
<
a
class
="
headerlink
"
href
="
#module-ast
"
title
="
このヘッドラインへのパーマリンク
"
>
¶
</
a
>
</
h1
>
<
p
>
<
strong
>
ソースコード:
</
strong
>
<
a
class
="
reference external
"
href
="
https://github.com/python/cpython/tree/3.6/Lib/ast.py
"
>
Lib/ast.py
</
a
>
</
p
>
<
hr
class
="
docutils
"
/>
<
p
>
<
a
class
="
reference internal
"
href
="
#module-ast
"
title
="
ast: Abstract Syntax Tree classes and manipulation.
"
>
<
code
class
="
xref py py-mod docutils literal
"
>
<
span
class
="
pre
"
>
ast
</
span
>
</
code
>
</
a
>
モジュールは、Python アプリケーションで Python の抽象構文木を処理しやすくするものです。抽象構文そのものは、Python のリリースごとに変化する可能性があります。このモジュールを使用すると、現在の文法をプログラム上で知る助けになるでしょう。
</
p
>
<
p
>
抽象構文木を作成するには、
<
code
class
="
xref py py-data docutils literal
"
>
<
span
class
="
pre
"
>
ast.PyCF_ONLY_AST
</
span
>
</
code
>
を組み込み関数
<
a
class
="
reference internal
"
href
="
functions.html#compile
"
title
="
compile
"
>
<
code
class
="
xref py py-func docutils literal
"
>
<
span
class
="
pre
"
>
compile()
</
span
>
</
code
>
</
a
>
のフラグとして渡すか、あるいはこのモジュールで提供されているヘルパー関数
<
a
class
="
reference internal
"
href
="
#ast.parse
"
title
="
ast.parse
"
>
<
code
class
="
xref py py-func docutils literal
"
>
<
span
class
="
pre
"
>
parse()
</
span
>
</
code
>
</
a
>
を使います。その結果は、
<
a
class
="
reference internal
"
href
="
#ast.AST
"
title
="
ast.AST
"
>
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.AST
</
span
>
</
code
>
</
a
>
を継承したクラスのオブジェクトのツリーとなります。抽象構文木は組み込み関数
<
a
class
="
reference internal
"
href
="
functions.html#compile
"
title
="
compile
"
>
<
code
class
="
xref py py-func docutils literal
"
>
<
span
class
="
pre
"
>
compile()
</
span
>
</
code
>
</
a
>
を使って Python コード・オブジェクトにコンパイルすることができます。
</
p
>
<
div
class
="
section
"
id
="
node-classes
"
>
<
h2
>
32.2.1. Node クラス
<
a
class
="
headerlink
"
href
="
#node-classes
"
title
="
このヘッドラインへのパーマリンク
"
>
¶
</
a
>
</
h2
>
<
dl
class
="
class
"
>
<
dt
id
="
ast.AST
"
>
<
em
class
="
property
"
>
class
</
em
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
AST
</
code
>
<
a
class
="
headerlink
"
href
="
#ast.AST
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
このクラスは全ての AST ノード・クラスの基底です。実際のノード・クラスは
<
a
class
="
reference internal
"
href
="
#abstract-grammar
"
>
<
span
class
="
std std-ref
"
>
後ほど
</
span
>
</
a
>
示す
<
code
class
="
file docutils literal
"
>
<
span
class
="
pre
"
>
Parser/Python.asdl
</
span
>
</
code
>
ファイルから派生したものです。これらのクラスは
<
code
class
="
xref py py-mod docutils literal
"
>
<
span
class
="
pre
"
>
_ast
</
span
>
</
code
>
C モジュールで定義され、
<
a
class
="
reference internal
"
href
="
#module-ast
"
title
="
ast: Abstract Syntax Tree classes and manipulation.
"
>
<
code
class
="
xref py py-mod docutils literal
"
>
<
span
class
="
pre
"
>
ast
</
span
>
</
code
>
</
a
>
にもエクスポートし直されています。
</
p
>
<
p
>
抽象文法の左辺のシンボル一つずつにそれぞれ一つのクラスがあります (たとえば
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.stmt
</
span
>
</
code
>
や
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.expr
</
span
>
</
code
>
)。それに加えて、右辺のコンストラクタ一つずつにそれぞれ一つのクラスがあり、これらのクラスは左辺のツリーのクラスを継承しています。たとえば、
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.BinOp
</
span
>
</
code
>
は
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.expr
</
span
>
</
code
>
から継承しています。代替を伴った生成規則 (production rules with alternatives) (別名 "sums") の場合、左辺は抽象クラスとなり、特定のコンストラクタ・ノードのインスタンスのみが作成されます。
</
p
>
<
dl
class
="
attribute
"
>
<
dt
id
="
ast.AST._fields
"
>
<
code
class
="
descname
"
>
_fields
</
code
>
<
a
class
="
headerlink
"
href
="
#ast.AST._fields
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
各具象クラスは属性
<
a
class
="
reference internal
"
href
="
#ast.AST._fields
"
title
="
ast.AST._fields
"
>
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
_fields
</
span
>
</
code
>
</
a
>
を持っており、すべての子ノードの名前をそこに保持しています。
</
p
>
<
p
>
具象クラスのインスタンスは、各子ノードに対してそれぞれひとつの属性を持っています。この属性は、文法で定義された型となります。たとえば
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.BinOp
</
span
>
</
code
>
のインスタンスは
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
left
</
span
>
</
code
>
という属性を持っており、その型は
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.expr
</
span
>
</
code
>
です。
</
p
>
<
p
>
これらの属性が、文法上 (クエスチョンマークを用いて) オプションであるとマークされている場合は、その値が
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
None
</
span
>
</
code
>
となることもあります。属性が0個以上の複数の値をとりうる場合 (アスタリスクでマークされている場合) は、値は Python のリストで表されます。全ての属性は AST を
<
a
class
="
reference internal
"
href
="
functions.html#compile
"
title
="
compile
"
>
<
code
class
="
xref py py-func docutils literal
"
>
<
span
class
="
pre
"
>
compile()
</
span
>
</
code
>
</
a
>
でコンパイルする際には存在しなければならず、そして妥当な値でなければなりません。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
attribute
"
>
<
dt
id
="
ast.AST.lineno
"
>
<
code
class
="
descname
"
>
lineno
</
code
>
<
a
class
="
headerlink
"
href
="
#ast.AST.lineno
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dt
id
="
ast.AST.col_offset
"
>
<
code
class
="
descname
"
>
col_offset
</
code
>
<
a
class
="
headerlink
"
href
="
#ast.AST.col_offset
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.expr
</
span
>
</
code
>
や
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.stmt
</
span
>
</
code
>
のサブクラスのインスタンスにはさらに
<
a
class
="
reference internal
"
href
="
#ast.AST.lineno
"
title
="
ast.AST.lineno
"
>
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
lineno
</
span
>
</
code
>
</
a
>
や
<
a
class
="
reference internal
"
href
="
#ast.AST.col_offset
"
title
="
ast.AST.col_offset
"
>
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
col_offset
</
span
>
</
code
>
</
a
>
といった属性があります。
<
a
class
="
reference internal
"
href
="
#ast.AST.lineno
"
title
="
ast.AST.lineno
"
>
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
lineno
</
span
>
</
code
>
</
a
>
はソーステキスト上の行番号 (1 から数え始めるので、最初の行の行番号は 1 となります)、そして
<
a
class
="
reference internal
"
href
="
#ast.AST.col_offset
"
title
="
ast.AST.col_offset
"
>
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
col_offset
</
span
>
</
code
>
</
a
>
はノードが生成した最初のトークンの UTF-8 バイトオフセットとなります。 UTF-8 オフセットが記録される理由は、パーサが内部で UTF-8 を使用するからです。
</
p
>
</
dd
>
</
dl
>
<
p
>
クラス
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.T
</
span
>
</
code
>
のコンストラクタは引数を次のように解析します:
</
p
>
<
ul
class
="
simple
"
>
<
li
>
位置引数があるとすれば、
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
T._fields
</
span
>
</
code
>
にあるのと同じだけの個数が無ければなりません。これらの引数はそこにある名前を持った属性として割り当てられます。
</
li
>
<
li
>
キーワード引数があるとすれば、それらはその名前の属性にその値を割り当てられます。
</
li
>
</
ul
>
<
p
>
たとえば、
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ast.UnaryOp
</
span
>
</
code
>
ノードを生成して属性を埋めるには、次のようにすることができます
</
p
>
<
div
class
="
highlight-python3
"
>
<
div
class
="
highlight
"
>
<
pre
>
<
span
>
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
n
"
>
ast
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
UnaryOp
</
span
>
<
span
class
="
p
"
>
()
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
op
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
n
"
>
ast
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
USub
</
span
>
<
span
class
="
p
"
>
()
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
operand
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
n
"
>
ast
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
Num
</
span
>
<
span
class
="
p
"
>
()
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
operand
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
n
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
5
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
operand
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
lineno
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
operand
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
col_offset
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
lineno
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
col_offset
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
</
pre
>
</
div
>
</
div
>
<
p
>
もしくはよりコンパクトにも書けます
</
p
>
<
div
class
="
highlight-python3
"
>
<
div
class
="
highlight
"
>
<
pre
>
<
span
>
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
n
"
>
ast
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
UnaryOp
</
span
>
<
span
class
="
p
"
>
(
</
span
>
<
span
class
="
n
"
>
ast
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
USub
</
span
>
<
span
class
="
p
"
>
(),
</
span
>
<
span
class
="
n
"
>
ast
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
Num
</
span
>
<
span
class
="
p
"
>
(
</
span
>
<
span
class
="
mi
"
>
5
</
span
>
<
span
class
="
p
"
>
,
</
span
>
<
span
class
="
n
"
>
lineno
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
p
"
>
,
</
span
>
<
span
class
="
n
"
>
col_offset
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
p
"
>
),
</
span
>
<
span
class
="
n
"
>
lineno
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
p
"
>
,
</
span
>
<
span
class
="
n
"
>
col_offset
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
mi
"
>
0
</
span
>
<
span
class
="
p
"
>
)
</
span
>
</
pre
>
</
div
>
</
div
>
</
dd
>
</
dl
>
</
div
>
<
div
class
="
section
"
id
="
abstract-grammar
"
>
<
span
id
="
id1
"
>
</
span
>
<
h2
>
32.2.2. 抽象文法 (Abstract Grammar)
<
a
class
="
headerlink
"
href
="
#abstract-grammar
"
title
="
このヘッドラインへのパーマリンク
"
>
¶
</
a
>
</
h2
>
<
p
>
抽象文法は、現在次のように定義されています:
</
p
>
<
div
class
="
highlight-none
"
>
<
div
class
="
highlight
"
>
<
pre
>
<
span
>
</
span
>
-- ASDL's 7 builtin types are:
-- identifier, int, string, bytes, object, singleton, constant
--
-- singleton: None, True or False
-- constant can be None, whereas None means "no value" for object.
module Python
{
mod = Module(stmt* body)
| Interactive(stmt* body)
| Expression(expr body)
-- not really an actual node but useful in Jython's typesystem.
| Suite(stmt* body)
stmt = FunctionDef(identifier name, arguments args,
stmt* body, expr* decorator_list, expr? returns)
| AsyncFunctionDef(identifier name, arguments args,
stmt* body, expr* decorator_list, expr? returns)
| ClassDef(identifier name,
expr* bases,
keyword* keywords,
stmt* body,
expr* decorator_list)
| Return(expr? value)
| Delete(expr* targets)
| Assign(expr* targets, expr value)
| AugAssign(expr target, operator op, expr value)
-- 'simple' indicates that we annotate simple name without parens
| AnnAssign(expr target, expr annotation, expr? value, int simple)
-- use 'orelse' because else is a keyword in target languages
| For(expr target, expr iter, stmt* body, stmt* orelse)
| AsyncFor(expr target, expr iter, stmt* body, stmt* orelse)
| While(expr test, stmt* body, stmt* orelse)
| If(expr test, stmt* body, stmt* orelse)
| With(withitem* items, stmt* body)
| AsyncWith(withitem* items, stmt* body)
| Raise(expr? exc, expr? cause)
| Try(stmt* body, excepthandler* handlers, stmt* orelse, stmt* finalbody)
| Assert(expr test, expr? msg)
| Import(alias* names)
| ImportFrom(identifier? module, alias* names, int? level)
| Global(identifier* names)
| Nonlocal(identifier* names)
| Expr(expr value)
| Pass | Break | Continue
-- XXX Jython will be different
-- col_offset is the byte offset in the utf8 string the parser uses
attributes (int lineno, int col_offset)
-- BoolOp() can use left & right?
expr = BoolOp(boolop op, expr* values)
| BinOp(expr left, operator op, expr right)
| UnaryOp(unaryop op, expr operand)
| Lambda(arguments args, expr body)
| IfExp(expr test, expr body, expr orelse)
| Dict(expr* keys, expr* values)
| Set(expr* elts)
| ListComp(expr elt, comprehension* generators)
| SetComp(expr elt, comprehension* generators)
| DictComp(expr key, expr value, comprehension* generators)
| GeneratorExp(expr elt, comprehension* generators)
-- the grammar constrains where yield expressions can occur
| Await(expr value)
| Yield(expr? value)
| YieldFrom(expr value)
-- need sequences for compare to distinguish between
-- x < 4 < 3 and (x < 4) < 3
| Compare(expr left, cmpop* ops, expr* comparators)
| Call(expr func, expr* args, keyword* keywords)
| Num(object n) -- a number as a PyObject.
| Str(string s) -- need to specify raw, unicode, etc?
| FormattedValue(expr value, int? conversion, expr? format_spec)
| JoinedStr(expr* values)
| Bytes(bytes s)
| NameConstant(singleton value)
| Ellipsis
| Constant(constant value)
-- the following expression can appear in assignment context
| Attribute(expr value, identifier attr, expr_context ctx)
| Subscript(expr value, slice slice, expr_context ctx)
| Starred(expr value, expr_context ctx)
| Name(identifier id, expr_context ctx)
| List(expr* elts, expr_context ctx)
| Tuple(expr* elts, expr_context ctx)
-- col_offset is the byte offset in the utf8 string the parser uses
attributes (int lineno, int col_offset)
expr_context = Load | Store | Del | AugLoad | AugStore | Param
slice = Slice(expr? lower, expr? upper, expr? step)
| ExtSlice(slice* dims)
| Index(expr value)
boolop = And | Or
operator = Add | Sub | Mult | MatMult | Div | Mod | Pow | LShift
| RShift | BitOr | BitXor | BitAnd | FloorDiv
unaryop = Invert | Not | UAdd | USub
cmpop = Eq | NotEq | Lt | LtE | Gt | GtE | Is | IsNot | In | NotIn
comprehension = (expr target, expr iter, expr* ifs, int is_async)
excepthandler = ExceptHandler(expr? type, identifier? name, stmt* body)
attributes (int lineno, int col_offset)
arguments = (arg* args, arg? vararg, arg* kwonlyargs, expr* kw_defaults,
arg? kwarg, expr* defaults)
arg = (identifier arg, expr? annotation)
attributes (int lineno, int col_offset)
-- keyword arguments supplied to call (NULL identifier for **kwargs)
keyword = (identifier? arg, expr value)
-- import name with optional 'as' alias.
alias = (identifier name, identifier? asname)
withitem = (expr context_expr, expr? optional_vars)
}
</
pre
>
</
div
>
</
div
>
</
div
>
<
div
class
="
section
"
id
="
ast-helpers
"
>
<
h2
>
32.2.3.
<
a
class
="
reference internal
"
href
="
#module-ast
"
title
="
ast: Abstract Syntax Tree classes and manipulation.
"
>
<
code
class
="
xref py py-mod docutils literal
"
>
<
span
class
="
pre
"
>
ast
</
span
>
</
code
>
</
a
>
ヘルパー
<
a
class
="
headerlink
"
href
="
#ast-helpers
"
title
="
このヘッドラインへのパーマリンク
"
>
¶
</
a
>
</
h2
>
<
p
>
ノード・クラスの他に、
<
a
class
="
reference internal
"
href
="
#module-ast
"
title
="
ast: Abstract Syntax Tree classes and manipulation.
"
>
<
code
class
="
xref py py-mod docutils literal
"
>
<
span
class
="
pre
"
>
ast
</
span
>
</
code
>
</
a
>
モジュールは以下のような抽象構文木をトラバースするためのユーティリティ関数やクラスも定義しています:
</
p
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.parse
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
parse
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
source
</
em
>
,
<
em
>
filename='<unknown>'
</
em
>
,
<
em
>
mode='exec'
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.parse
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
em
>
source
</
em
>
を解析して AST ノードにします。
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
compile(source,
</
span
>
<
span
class
="
pre
"
>
filename,
</
span
>
<
span
class
="
pre
"
>
mode,
</
span
>
<
span
class
="
pre
"
>
ast.PyCF_ONLY_AST)
</
span
>
</
code
>
と等価です。
</
p
>
<
div
class
="
admonition warning
"
>
<
p
class
="
first admonition-title
"
>
警告
</
p
>
<
p
class
="
last
"
>
十分に大きい文字列や複雑な文字列によって Python の抽象構文木コンパイラのスタックの深さの限界を越えることで、 Python インタプリタをクラッシュさせることができます。
</
p
>
</
div
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.literal_eval
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
literal_eval
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node_or_string
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.literal_eval
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
式ノードまたは Python のリテラルまたはコンテナのディスプレイ表現を表す文字列を安全に評価します。与えられる文字列またはノードは次のリテラルのみからなるものに限られます: 文字列、バイト列、数、タプル、リスト、辞書、集合、ブール値、
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
None
</
span
>
</
code
>
。
</
p
>
<
p
>
この関数は Python の式を含んだ信頼出来ない出どころからの文字列を、値自身を解析することなしに安全に評価するのに使えます。この関数は、例えば演算や添え字を含んだ任意の複雑な表現を評価するのには使えません。
</
p
>
<
div
class
="
admonition warning
"
>
<
p
class
="
first admonition-title
"
>
警告
</
p
>
<
p
class
="
last
"
>
十分に大きい文字列や複雑な文字列によって Python の抽象構文木コンパイラのスタックの深さの限界を越えることで、 Python インタプリタをクラッシュさせることができます。
</
p
>
</
div
>
<
div
class
="
versionchanged
"
>
<
p
>
<
span
class
="
versionmodified
"
>
バージョン 3.2 で変更:
</
span
>
バイト列リテラルと集合リテラルが受け取れるようになりました。
</
p
>
</
div
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.get_docstring
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
get_docstring
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
,
<
em
>
clean=True
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.get_docstring
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
与えられた
<
em
>
node
</
em
>
(これは
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
FunctionDef
</
span
>
</
code
>
,
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
ClassDef
</
span
>
</
code
>
,
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
Module
</
span
>
</
code
>
のいずれかのノードでなければなりません) のドキュメント文字列を返します。もしドキュメント文字列が無ければ
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
None
</
span
>
</
code
>
を返します。
<
em
>
clean
</
em
>
が真ならば、ドキュメント文字列のインデントを
<
a
class
="
reference internal
"
href
="
inspect.html#inspect.cleandoc
"
title
="
inspect.cleandoc
"
>
<
code
class
="
xref py py-func docutils literal
"
>
<
span
class
="
pre
"
>
inspect.cleandoc()
</
span
>
</
code
>
</
a
>
を用いて一掃します。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.fix_missing_locations
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
fix_missing_locations
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.fix_missing_locations
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
a
class
="
reference internal
"
href
="
functions.html#compile
"
title
="
compile
"
>
<
code
class
="
xref py py-func docutils literal
"
>
<
span
class
="
pre
"
>
compile()
</
span
>
</
code
>
</
a
>
はノード・ツリーをコンパイルする際、
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
lineno
</
span
>
</
code
>
と
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
col_offset
</
span
>
</
code
>
両属性をサポートする全てのノードに対しそれが存在するものと想定します。生成されたノードに対しこれらを埋めて回るのはどちらかというと退屈な作業なので、このヘルパーが再帰的に二つの属性がセットされていないものに親ノードと同じ値をセットしていきます。再帰の出発点が
<
em
>
node
</
em
>
です。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.increment_lineno
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
increment_lineno
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
,
<
em
>
n=1
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.increment_lineno
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
em
>
node
</
em
>
から始まるツリーの全てのノードの行番号を
<
em
>
n
</
em
>
ずつ増やします。これはファイルの中で別の場所に「コードを動かす」ときに便利です。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.copy_location
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
copy_location
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
new_node
</
em
>
,
<
em
>
old_node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.copy_location
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
ソースの場所 (
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
lineno
</
span
>
</
code
>
と
<
code
class
="
xref py py-attr docutils literal
"
>
<
span
class
="
pre
"
>
col_offset
</
span
>
</
code
>
) を
<
em
>
old_node
</
em
>
から
<
em
>
new_node
</
em
>
に可能ならばコピーし、
<
em
>
new_node
</
em
>
を返します。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.iter_fields
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
iter_fields
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.iter_fields
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
em
>
node
</
em
>
にある
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
node._fields
</
span
>
</
code
>
のそれぞれのフィールドを
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
(フィールド名,
</
span
>
<
span
class
="
pre
"
>
値)
</
span
>
</
code
>
のタプルとして yield します。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.iter_child_nodes
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
iter_child_nodes
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.iter_child_nodes
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
em
>
node
</
em
>
の直接の子ノード全てを yield します。すなわち、yield されるのは、ノードであるような全てのフィールドおよびノードのリストであるようなフィールドの全てのアイテムです。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.walk
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
walk
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.walk
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
em
>
node
</
em
>
の全ての子孫ノード(
<
em
>
node
</
em
>
自体を含む)を再帰的に yield します。順番は決められていません。この関数はノードをその場で変更するだけで文脈を気にしないような場合に便利です。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
class
"
>
<
dt
id
="
ast.NodeVisitor
"
>
<
em
class
="
property
"
>
class
</
em
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
NodeVisitor
</
code
>
<
a
class
="
headerlink
"
href
="
#ast.NodeVisitor
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
抽象構文木を渡り歩いてビジター関数を見つけたノードごとに呼び出すノード・ビジターの基底クラスです。この関数は
<
a
class
="
reference internal
"
href
="
#ast.NodeVisitor.visit
"
title
="
ast.NodeVisitor.visit
"
>
<
code
class
="
xref py py-meth docutils literal
"
>
<
span
class
="
pre
"
>
visit()
</
span
>
</
code
>
</
a
>
メソッドに送られる値を返してもかまいません。
</
p
>
<
p
>
このクラスはビジター・メソッドを付け加えたサブクラスを派生させることを意図しています。
</
p
>
<
dl
class
="
method
"
>
<
dt
id
="
ast.NodeVisitor.visit
"
>
<
code
class
="
descname
"
>
visit
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.NodeVisitor.visit
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
ノードを訪れます。デフォルトの実装では
<
code
class
="
samp docutils literal
"
>
<
span
class
="
pre
"
>
self.visit_
</
span
>
<
em
>
<
span
class
="
pre
"
>
classname
</
span
>
</
em
>
</
code
>
というメソッド (ここで
<
em
>
classname
</
em
>
はノードのクラス名です) を呼び出すか、そのメソッドがなければ
<
a
class
="
reference internal
"
href
="
#ast.NodeVisitor.generic_visit
"
title
="
ast.NodeVisitor.generic_visit
"
>
<
code
class
="
xref py py-meth docutils literal
"
>
<
span
class
="
pre
"
>
generic_visit()
</
span
>
</
code
>
</
a
>
を呼び出します。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
method
"
>
<
dt
id
="
ast.NodeVisitor.generic_visit
"
>
<
code
class
="
descname
"
>
generic_visit
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.NodeVisitor.generic_visit
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
このビジターはノードの全ての子について
<
a
class
="
reference internal
"
href
="
#ast.NodeVisitor.visit
"
title
="
ast.NodeVisitor.visit
"
>
<
code
class
="
xref py py-meth docutils literal
"
>
<
span
class
="
pre
"
>
visit()
</
span
>
</
code
>
</
a
>
を呼び出します。
</
p
>
<
p
>
注意して欲しいのは、専用のビジター・メソッドを具えたノードの子ノードは、このビジターが
<
a
class
="
reference internal
"
href
="
#ast.NodeVisitor.generic_visit
"
title
="
ast.NodeVisitor.generic_visit
"
>
<
code
class
="
xref py py-meth docutils literal
"
>
<
span
class
="
pre
"
>
generic_visit()
</
span
>
</
code
>
</
a
>
を呼び出すかそれ自身で子ノードを訪れない限り訪れられないということです。
</
p
>
</
dd
>
</
dl
>
<
p
>
トラバースの途中でノードを変化させたいならば
<
a
class
="
reference internal
"
href
="
#ast.NodeVisitor
"
title
="
ast.NodeVisitor
"
>
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
NodeVisitor
</
span
>
</
code
>
</
a
>
を使ってはいけません。そうした目的のために変更を許す特別なビジター (
<
a
class
="
reference internal
"
href
="
#ast.NodeTransformer
"
title
="
ast.NodeTransformer
"
>
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
NodeTransformer
</
span
>
</
code
>
</
a
>
) があります。
</
p
>
</
dd
>
</
dl
>
<
dl
class
="
class
"
>
<
dt
id
="
ast.NodeTransformer
"
>
<
em
class
="
property
"
>
class
</
em
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
NodeTransformer
</
code
>
<
a
class
="
headerlink
"
href
="
#ast.NodeTransformer
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
a
class
="
reference internal
"
href
="
#ast.NodeVisitor
"
title
="
ast.NodeVisitor
"
>
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
NodeVisitor
</
span
>
</
code
>
</
a
>
のサブクラスで抽象構文木を渡り歩きながらノードを変更することを許すものです。
</
p
>
<
p
>
<
a
class
="
reference internal
"
href
="
#ast.NodeTransformer
"
title
="
ast.NodeTransformer
"
>
<
code
class
="
xref py py-class docutils literal
"
>
<
span
class
="
pre
"
>
NodeTransformer
</
span
>
</
code
>
</
a
>
は抽象構文木(AST)を渡り歩き、ビジター・メソッドの戻り値を使って古いノードを置き換えたり削除したりします。ビジター・メソッドの戻り値が
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
None
</
span
>
</
code
>
ならば、ノードはその場から取り去られ、そうでなければ戻り値で置き換えられます。置き換えない場合は戻り値が元のノードそのものであってもかまいません。
</
p
>
<
p
>
それでは例を示しましょう。Name (たとえば
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
foo
</
span
>
</
code
>
) を見つけるたび全て
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
data['foo']
</
span
>
</
code
>
に書き換える変換器 (transformer) です:
</
p
>
<
div
class
="
highlight-python3
"
>
<
div
class
="
highlight
"
>
<
pre
>
<
span
>
</
span
>
<
span
class
="
k
"
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class
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="
nc
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(
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="
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):
</
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def
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class
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(
</
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bp
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self
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class
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return
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copy_location
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="
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>
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</
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="
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span
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="
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>
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</
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>
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="
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</
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>
<
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="
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>
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</
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>
<
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class
="
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=
</
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span
class
="
n
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>
node
</
span
>
<
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class
="
o
"
>
.
</
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>
<
span
class
="
n
"
>
id
</
span
>
<
span
class
="
p
"
>
)),
</
span
>
<
span
class
="
n
"
>
ctx
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
ctx
</
span
>
<
span
class
="
p
"
>
),
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
p
"
>
)
</
span
>
</
pre
>
</
div
>
</
div
>
<
p
>
操作しようとしているノードが子ノードを持つならば、その子ノードの変形も自分で行うか、またはそのノードに対し最初に
<
code
class
="
xref py py-meth docutils literal
"
>
<
span
class
="
pre
"
>
generic_visit()
</
span
>
</
code
>
メソッドを呼び出すか、それを行うのはあなたの責任だということを肝に銘じましょう。
</
p
>
<
p
>
文のコレクションであるようなノード (全ての文のノードが当てはまります) に対して、このビジターは単独のノードではなくノードのリストを返すかもしれません。
</
p
>
<
p
>
たいてい、変換器の使い方は次のようになります:
</
p
>
<
div
class
="
highlight-python3
"
>
<
div
class
="
highlight
"
>
<
pre
>
<
span
>
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
o
"
>
=
</
span
>
<
span
class
="
n
"
>
YourTransformer
</
span
>
<
span
class
="
p
"
>
()
</
span
>
<
span
class
="
o
"
>
.
</
span
>
<
span
class
="
n
"
>
visit
</
span
>
<
span
class
="
p
"
>
(
</
span
>
<
span
class
="
n
"
>
node
</
span
>
<
span
class
="
p
"
>
)
</
span
>
</
pre
>
</
div
>
</
div
>
</
dd
>
</
dl
>
<
dl
class
="
function
"
>
<
dt
id
="
ast.dump
"
>
<
code
class
="
descclassname
"
>
ast.
</
code
>
<
code
class
="
descname
"
>
dump
</
code
>
<
span
class
="
sig-paren
"
>
(
</
span
>
<
em
>
node
</
em
>
,
<
em
>
annotate_fields=True
</
em
>
,
<
em
>
include_attributes=False
</
em
>
<
span
class
="
sig-paren
"
>
)
</
span
>
<
a
class
="
headerlink
"
href
="
#ast.dump
"
title
="
この定義へのパーマリンク
"
>
¶
</
a
>
</
dt
>
<
dd
>
<
p
>
<
em
>
node
</
em
>
中のツリーのフォーマットされたダンプを返します。主な使い道はデバッグです。返される文字列は名前とフィールドの値を表示します。これを使うとコードは評価できなくなりますので、評価が必要ならば
<
em
>
annotate_fields
</
em
>
に
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
False
</
span
>
</
code
>
をセットしなければなりません。行番号や列オフセットのような属性はデフォルトではダンプされません。これが欲しければ、
<
em
>
include_attributes
</
em
>
を
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
True
</
span
>
</
code
>
にセットすることができます。
</
p
>
</
dd
>
</
dl
>
<
div
class
="
admonition seealso
"
>
<
p
class
="
first admonition-title
"
>
参考
</
p
>
<
p
class
="
last
"
>
外部ドキュメント
<
a
class
="
reference external
"
href
="
https://greentreesnakes.readthedocs.org/
"
>
Green Tree Snakes
</
a
>
には Python AST についての詳細が書かれています。
</
p
>
</
div
>
</
div
>
</
div
>
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div
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<
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<
li
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<
a
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reference internal
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href
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#
"
>
32.2.
<
code
class
="
docutils literal
"
>
<
span
class
="
pre
"
>
ast
</
span
>
</
code
>
— 抽象構文木
</
a
>
<
ul
>
<
li
>
<
a
class
="
reference internal
"
href
="
#node-classes
"
>
32.2.1. Node クラス
</
a
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<
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reference internal
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href
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#abstract-grammar
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32.2.2. 抽象文法 (Abstract Grammar)
</
a
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<
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<
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class
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reference internal
"
href
="
#ast-helpers
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>
32.2.3.
<
code
class
="
docutils literal
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<
span
class
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pre
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ast
</
span
>
</
code
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ヘルパー
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<
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前のトピックへ
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class
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topless
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<
a
href
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title
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32.1.
<
code
class
="
docutils literal
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span
class
="
pre
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parser
</
span
>
</
code
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— Python 解析木にアクセスする
</
a
>
</
p
>
<
h4
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次のトピックへ
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<
p
class
="
topless
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<
a
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code
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