Merge pull request #609 from realpython/expressions-vs-statements

Materials for Python Expressions vs Statements

expressions-vs-statements/README.md

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+# Expression vs Statement in Python: What's the Difference?
+
+This folder contains sample code from the Real Python tutorial [Expression vs Statement in Python: What's the Difference?](https://realpython.com/python-expression-vs-statement/)
+
+## Code Inspector
+
+Identify whether a piece of Python code is an expression or a statement:
+
+```shell
+$ python code_inspector.py
+Type a Python code snippet or leave empty to exit.
+>>> yield
+statement
+>>> (yield)
+expression
+>>> 2 +
+invalid
+```
+
+## GUI App
+
+Register a lambda expression as a callback, which delegates to a function with statements:
+
+```shell
+$ python gui_app.py
+```
+
+## Echo Program
+
+Compile with a C compiler and pipe stdin to the echo program:
+
+```shell
+$ gcc echo.c -o echo.x
+$ echo "Hello, World!" | ./echo.x
+Hello, World!
+```
+
+## HEX Reader
+
+Read a binary file and display its bytes in hexadecimal format:
+
+```shell
+$ python hex_reader.py /path/to/HelloJava.class --columns 8
+ca fe ba be 00 00 00 41
+00 0f 0a 00 02 00 03 07
+00 04 0c 00 05 00 06 01
+(...)
+```
+
+## Generators
+
+Generate a random signal and use a low-pass filter to make it smooth:
+
+```shell
+$ python generators.py 
+-0.96: -0.96
+-0.81: -0.89
+-0.52: -0.67
+ 0.22: -0.15
+ 0.51:  0.37
+ 0.40:  0.46
+-0.08:  0.16
+-0.24: -0.16
+ 0.80:  0.28
+ 0.47:  0.64
+```

expressions-vs-statements/code_inspector.py

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+import ast
+
+
+def main():
+    print("Type a Python code snippet or leave empty to exit.")
+    while code := input(">>> "):
+        print(describe(code))
+
+
+def describe(code):
+    if valid(code, mode="eval"):
+        return "expression"
+    elif valid(code, mode="exec"):
+        return "statement"
+    else:
+        return "invalid"
+
+
+def valid(code, mode):
+    try:
+        ast.parse(code, mode=mode)
+        return True
+    except SyntaxError:
+        return False
+
+
+if __name__ == "__main__":
+    try:
+        main()
+    except EOFError:
+        pass

expressions-vs-statements/echo.c

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+#include <stdio.h>
+
+int main() {
+    int x;
+    while (x = fgetc(stdin)) {
+        if (x == EOF)
+            break;
+        putchar(x);
+    }
+    return 0;
+}

expressions-vs-statements/generators.py

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+import random
+
+
+def main():
+    lf = lowpass_filter()
+    lf.send(None)
+    for value in generate_noise(10):
+        print(f"{value:>5.2f}: {lf.send(value):>5.2f}")
+
+
+def generate_noise(size):
+    for _ in range(size):
+        yield 2 * random.random() - 1
+
+
+def lowpass_filter():
+    a = yield
+    b = yield a
+    while True:
+        a, b = b, (yield (a + b) / 2)
+
+
+if __name__ == "__main__":
+    main()

expressions-vs-statements/gui_app.py

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+import tkinter as tk
+
+
+def main():
+    window = tk.Tk()
+    button = tk.Button(window, text="Click", command=lambda: on_click(42))
+    button.pack(padx=10, pady=10)
+    window.mainloop()
+
+
+def on_click(age):
+    if age > 18:
+        print("You're an adult.")
+    else:
+        print("You're a minor.")
+
+
+if __name__ == "__main__":
+    main()

expressions-vs-statements/hex_reader.py

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+import argparse
+import itertools
+
+MAX_BYTES = 1024
+
+
+def main(args):
+    buffer = bytearray()
+    with open(args.path, mode="rb") as file:
+        while chunk := file.read(MAX_BYTES):
+            buffer.extend(chunk)
+    for row in itertools.batched(buffer, args.columns):
+        print(" ".join(f"{byte:02x}" for byte in row))
+
+
+def parse_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("path")
+    parser.add_argument("-c", "--columns", type=int, default=16)
+    return parser.parse_args()
+
+
+if __name__ == "__main__":
+    main(parse_args())