参数

参数

Click 支持两种类型的脚本参数: 选项和参数。命令行脚本的作者通常在使用哪个脚本时会有一些混淆，所以这里是对这些差异的简要概述。正如其名称所示，选项是可选的。虽然参数在合理的范围内是可选的，但是它们在选择的方式上会受到更多的限制。

为了帮助您在选项和参数之间做出决定，建议仅使用参数，例如转到子命令或输入文件名, / , URLs，然后让所有其他选项成为选项。

差异

参数功能略少于选项。以下功能仅适用于选项:

选项可自动提示缺少输入
选项可作为标志（布尔值或其他）
选项值可以从环境变量中拉出来，但参数不能
选项能完整记录在帮助页面中，但参数不能（这显而易见，因为参数可能过于具体而不能自动记录）
另一方面，与选项不同，参数可以接受任意数量的参数。选项可以严格地只接受固定数量的参数（默认为1）。

参数类型

参数可以是不同的类型。类型可以用不同的行为来实现，有些是开箱即用的:

str / click.STRING:: 表示unicode字符串的默认参数类型。
int / click.INT:: 只接受整数的参数。
float / click.FLOAT:: 只接受浮点值的参数。
bool / click.BOOL:: 接受布尔值的参数。这是自动使用布尔值的标志。如果字符值是: 1, yes, y和 true 转化为 True ； 0, no, n ， false 转化为 False 。
click.UUID:: 接受UUID值的参数。这不是自动识别，而是表示为 uuid.UUID.

class click.File(mode='r', encoding=None, errors='strict', lazy=None, atomic=False)

Declares a parameter to be a file for reading or writing. The fileis automatically closed once the context tears down (after the commandfinished working).

Files can be opened for reading or writing. The special value -indicates stdin or stdout depending on the mode.

By default, the file is opened for reading text data, but it can also beopened in binary mode or for writing. The encoding parameter can be usedto force a specific encoding.

The lazy flag controls if the file should be opened immediately orupon first IO. The default is to be non lazy for standard input andoutput streams as well as files opened for reading, lazy otherwise.

Starting with Click 2.0, files can also be opened atomically in whichcase all writes go into a separate file in the same folder and uponcompletion the file will be moved over to the original location. Thisis useful if a file regularly read by other users is modified.

See 文件参数 for more information.

class click.Path(exists=False, file_okay=True, dir_okay=True, writable=False, readable=True, resolve_path=False, allow_dash=False, path_type=None)

The path type is similar to the File type but it performsdifferent checks. First of all, instead of returning an open filehandle it returns just the filename. Secondly, it can perform variousbasic checks about what the file or directory should be.

在 6.0 版更改: allow_dash was added.

参数:

参数:	exists — if set to true, the file or directory needs to exist forthis value to be valid. If this is not required and afile does indeed not exist, then all further checks aresilently skipped. file_okay — controls if a file is a possible value. dir_okay — controls if a directory is a possible value. writable — if true, a writable check is performed. readable — if true, a readable check is performed. resolve_path — if this is true, then the path is fully resolvedbefore the value is passed onwards. This meansthat it's absolute and symlinks are resolved. allow_dash — If this is set to True, a single dash to indicatestandard streams is permitted. type — optionally a string type that should be used torepresent the path. The default is None whichmeans the return value will be either bytes orunicode depending on what makes most sense given theinput data Click deals with.

exists — if set to true, the file or directory needs to exist forthis value to be valid. If this is not required and afile does indeed not exist, then all further checks aresilently skipped.
file_okay — controls if a file is a possible value.
dir_okay — controls if a directory is a possible value.
writable — if true, a writable check is performed.
readable — if true, a readable check is performed.
resolve_path — if this is true, then the path is fully resolvedbefore the value is passed onwards. This meansthat it's absolute and symlinks are resolved.
allow_dash — If this is set to True, a single dash to indicatestandard streams is permitted.
type — optionally a string type that should be used torepresent the path. The default is None whichmeans the return value will be either bytes orunicode depending on what makes most sense given theinput data Click deals with.

class click.Choice(choices): The choice type allows a value to be checked against a fixed set ofsupported values. All of these values have to be strings.
See 选择选项 for an example.

class click.IntRange(min=None, max=None, clamp=False)

A parameter that works similar to click.INT but restrictsthe value to fit into a range. The default behavior is to fail if thevalue falls outside the range, but it can also be silently clampedbetween the two edges.

See 范围选项 for an example.

自定义参数类型可以通过子类实现 click.ParamType 。对于简单的情况，也支持传递一个失败的 ValueError Python函数，尽管不鼓励这么做。

参数名称

参数（包括选项和参数）都接受一些参数声明的位置参数。每个带有单个短划线的字符串都被添加为短参数; 每个字符串都以一个双破折号开始。如果添加一个没有任何破折号的字符串，它将成为内部参数名称，也被用作变量名称。

如果一个参数没有给出一个没有破折号的名字, 那么通过采用最长的参数并将所有的破折号转换为下划线来自动生成一个名字。如果一个有 ('-f', '—foo-bar') 的选项，那么该参数名被设置为 foo_bar ，如果一个有 ('-x',) 的选项, 那么该参数名被设置为 x ，如果一个有 ('-f', '—filename', 'dest') 的选项，那么该参数名被设置为 dest 。

实现自定义类型

要实现一个自定义类型，你需要继承这个 ParamType 类类型可以调用有或没有上下文和参数对象，这就是为什么他们需要能够处理这个问题。

下面的代码实现了一个整数类型，除了普通整数之外，还接受十六进制和八进制数字，并将它们转换为常规整数：:

import click
 
class BasedIntParamType(click.ParamType):
    name = 'integer'
 
    def convert(self, value, param, ctx):
        try:
            if value[:2].lower() == '0x':
                return int(value[2:], 16)
            elif value[:1] == '0':
                return int(value, 8)
            return int(value, 10)
        except ValueError:
            self.fail('%s is not a valid integer' % value, param, ctx)
 
BASED_INT = BasedIntParamType()

如你所见, 一个子类需要实现这个 ParamType.convert() 方法，并且可以选择提供这个 ParamType.name 属性。后者可用于文档的目的。