complete cat exercise

Author: enjoy15

implement-shell-tools/cat/cat.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+
+import sys
+
+def cat_file(file, options, line_number):
+    try:
+        with open(file, 'r', encoding='utf-8') as f:
+            lines = f.readlines()
+
+        for line in lines:
+            if options['number_non_blank'] and line.strip():
+                print(f"{line_number:6}\t{line}", end='')
+                line_number += 1
+            elif options['number_all']:
+                print(f"{line_number:6}\t{line}", end='')
+                line_number += 1
+            else:
+                print(line, end='')
+
+        return line_number
+    except FileNotFoundError:
+        print(f"cat: {file}: No such file or directory", file=sys.stderr)
+        sys.exit(1)
+
+def main():
+    args = sys.argv[1:]
+    options = {
+        'number_all': False,
+        'number_non_blank': False,
+    }
+
+    files = []
+
+    for arg in args:
+        if arg == '-n':
+            options['number_all'] = True
+        elif arg == '-b':
+            options['number_non_blank'] = True
+        else:
+            files.append(arg)
+
+    if not files:
+        print("Usage: cat [-n | -b] <file>...", file=sys.stderr)
+        sys.exit(1)
+
+    line_number = 1
+    for file in files:
+        line_number = cat_file(file, options, line_number)
+
+if __name__ == "__main__":
+    main()