阅读argparse文档

python/argparse.md

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+- [argparse](#argparse)
+  - [位置参数](#位置参数)
+  - [可选项参数](#可选项参数)
+    - [store\_true](#store_true)
+    - [短选项](#短选项)
+    - [为可选参数指定type](#为可选参数指定type)
+    - [choice](#choice)
+    - [count](#count)
+    - [add\_mutually\_exclusive\_group](#add_mutually_exclusive_group)
+  - [指定命令行描述](#指定命令行描述)
+
+
+# argparse
+通过argparse模块，可以针对命令行参数进行解析。
+
+## 位置参数
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("echo", help="echo the string you use here")
+args = parser.parse_args()
+print(args.echo)
+```
+
+## 可选项参数
+### store_true
+通过将action指定为`store_true`，当命令行参数中出现该可选参数时，`args.{opt_flag_name}`值为True，否则为False
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("--verbose", help="increase output verbosity",
+                    action="store_true")
+args = parser.parse_args()
+if args.verbose:
+    print("verbosity turned on")
+```
+
+### 短选项
+可以为可选参数指定段选项，令`-v`和`--verbose`达到相同的效果
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("-v", "--verbose", help="increase output verbosity",
+                    action="store_true")
+args = parser.parse_args()
+if args.verbose:
+    print("verbosity turned on")
+```
+
+### 为可选参数指定type
+为可选参数指定type后，可选参数后必须跟随一个整数值。
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("square", type=int,
+                    help="display a square of a given number")
+parser.add_argument("-v", "--verbosity", type=int,
+                    help="increase output verbosity")
+args = parser.parse_args()
+answer = args.square**2
+if args.verbosity == 2:
+    print(f"the square of {args.square} equals {answer}")
+elif args.verbosity == 1:
+    print(f"{args.square}^2 == {answer}")
+else:
+    print(answer)
+```
+### choice
+可以通过为可选参数指定`choice`来限定可选参数值范围
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("square", type=int,
+                    help="display a square of a given number")
+parser.add_argument("-v", "--verbosity", type=int, choices=[0, 1, 2],
+                    help="increase output verbosity")
+args = parser.parse_args()
+answer = args.square**2
+if args.verbosity == 2:
+    print(f"the square of {args.square} equals {answer}")
+elif args.verbosity == 1:
+    print(f"{args.square}^2 == {answer}")
+else:
+    print(answer)
+```
+### count
+可以将可选参数的action指定为`count`，此时`args.{opt_flag_name}`的值将为该可选参数出现的次数，如未指定该可选参数，值为None。
+
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("square", type=int,
+                    help="display the square of a given number")
+parser.add_argument("-v", "--verbosity", action="count",
+                    help="increase output verbosity")
+args = parser.parse_args()
+answer = args.square**2
+if args.verbosity == 2:
+    print(f"the square of {args.square} equals {answer}")
+elif args.verbosity == 1:
+    print(f"{args.square}^2 == {answer}")
+else:
+    print(answer)
+```
+
+如果想要在未指定可选参数时，为该参数指定一个默认值，可以使用`default`：
+```py
+import argparse
+parser = argparse.ArgumentParser()
+parser.add_argument("square", type=int,
+                    help="display a square of a given number")
+parser.add_argument("-v", "--verbosity", action="count", default=0,
+                    help="increase output verbosity")
+args = parser.parse_args()
+answer = args.square**2
+if args.verbosity >= 2:
+    print(f"the square of {args.square} equals {answer}")
+elif args.verbosity >= 1:
+    print(f"{args.square}^2 == {answer}")
+else:
+    print(answer)
+```
+
+### add_mutually_exclusive_group
+通过`add_mutually_exclusive_group`，可以指定彼此之间相互冲突的选项：
+```py
+import argparse
+
+parser = argparse.ArgumentParser()
+group = parser.add_mutually_exclusive_group()
+group.add_argument("-v", "--verbose", action="store_true")
+group.add_argument("-q", "--quiet", action="store_true")
+parser.add_argument("x", type=int, help="the base")
+parser.add_argument("y", type=int, help="the exponent")
+args = parser.parse_args()
+answer = args.x**args.y
+
+if args.quiet:
+    print(answer)
+elif args.verbose:
+    print(f"{args.x} to the power {args.y} equals {answer}")
+else:
+    print(f"{args.x}^{args.y} == {answer}")
+```
+此时，`-v`和`-q`为冲突的可选参数，无法同时指定
+
+## 指定命令行描述
+```py
+import argparse
+
+parser = argparse.ArgumentParser(description="calculate X to the power of Y")
+group = parser.add_mutually_exclusive_group()
+group.add_argument("-v", "--verbose", action="store_true")
+group.add_argument("-q", "--quiet", action="store_true")
+parser.add_argument("x", type=int, help="the base")
+parser.add_argument("y", type=int, help="the exponent")
+args = parser.parse_args()
+answer = args.x**args.y
+
+if args.quiet:
+    print(answer)
+elif args.verbose:
+    print(f"{args.x} to the power {args.y} equals {answer}")
+else:
+    print(f"{args.x}^{args.y} == {answer}")
+```