```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

在底层，`open("./somefile.txt")`创建了一个被称为"上下文管理器"的对象。

当 `with` 代码块结束时，它会确保关闭文件，即使发生了异常也是如此。

当你使用 `yield` 创建一个依赖项时，**FastAPI** 会在内部将其转换为上下文管理器，并与其他相关工具结合使用。

### 在使用 `yield` 的依赖项中使用上下文管理器

!important;\n    display: inline-flex !important;\n  }\n}\n\n@media print {\n  .d-print-none {\n    display: none !important;\n  }\n  .d-print-inline {\n    display: inline !important;\n  }\n  .d-print-inline-block {\n    display: inline-block !important;\n  }\n  .d-print-block {\n    display: block !important;\n  }\n  .d-print-table {\n    display: table !important;\n  }\n  .d-print-table-row {\n    display: table-row !important;\n  }\n  .d-print-table-cell {\n    display: table-cell !important;\n  }\n  .d-print-flex...

!important;\n    display: inline-flex !important;\n  }\n}\n\n@media print {\n  .d-print-none {\n    display: none !important;\n  }\n  .d-print-inline {\n    display: inline !important;\n  }\n  .d-print-inline-block {\n    display: inline-block !important;\n  }\n  .d-print-block {\n    display: block !important;\n  }\n  .d-print-table {\n    display: table !important;\n  }\n  .d-print-table-row {\n    display: table-row !important;\n  }\n  .d-print-table-cell {\n    display: table-cell !important;\n  }\n  .d-print-flex...

```Python
with open("./somefile.txt") as f:
    contents = f.read()
    print(contents)
```

Por baixo dos panos, o código `open("./somefile.txt")` cria um objeto que é chamado de "Gerenciador de Contexto".

invoking the C compiler to compile the C parts of the package.

The following options are available when running cgo directly:

	-V
		Print cgo version and exit.
	-debug-define
		Debugging option. Print #defines.
	-debug-gcc
		Debugging option. Trace C compiler execution and output.
	-dynimport file
		Write list of symbols imported by file. Write to

```Python hl_lines="2-5  15  21"
{!../../docs_src/handling_errors/tutorial006.py!}
```

		for idx, d := range v {
			if idx > 0 {
				writer.WriteByte(',')
			}
			stmt.DB.Dialector.QuoteTo(writer, d)
		}
		writer.WriteByte(')')
	default:
		stmt.DB.Dialector.QuoteTo(writer, fmt.Sprint(field))
	}
}

// Quote returns quoted value
func (stmt *Statement) Quote(field interface{}) string {
	var builder strings.Builder
	stmt.QuoteTo(&builder, field)
	return builder.String()
}

```Python hl_lines="2-5  15  21"
{!../../docs_src/handling_errors/tutorial006.py!}
```

errors.invalid_header_for_request_file=Invalid header: {0}
errors.could_not_delete_logged_in_user=Could not delete logged in user.
errors.unauthorized_request=Unauthorized request.
errors.failed_to_print_thread_dump=Failed to print thread dump.
errors.file_is_not_supported={0} is not supported.
errors.plugin_file_is_not_found={0} is not found.
errors.failed_to_install_plugin=Failed to install {0}.

errors.invalid_header_for_request_file=Invalid header: {0}
errors.could_not_delete_logged_in_user=Could not delete logged in user.
errors.unauthorized_request=Unauthorized request.
errors.failed_to_print_thread_dump=Failed to print thread dump.
errors.file_is_not_supported={0} is not supported.
errors.plugin_file_is_not_found={0} is not found.
errors.failed_to_install_plugin=Failed to install {0}.