A few improvements

.gitignore

@@ -0,0 +1,2 @@
+*:Zone.Identifier
+

requirements.txt

@@ -0,0 +1,2 @@
+scikit-rf
+matplotlib

stospice.py

@@ -1,47 +1,79 @@
+#!/usr/bin/env python
 
-def stospice(filename, name, f, s, z0):
+
+
+def extract_comments(infilename):
+    comments = []
+    with open(infilename, "r") as ifd:
+        lines = ifd.read().splitlines()
+    for line in lines:
+        line = line.strip()
+        if not line.startswith("!"):
+            continue
+        comments.append(f"* {line[1:]}")
+    return comments
+
+
+def stospice(filename, name, f, s, z0, comments=None):
     dim = 100
     nports = s.shape[1]
     if nports > dim - 2:
         raise SystemExit('too many ports')
     z0 = z0 if hasattr(z0, '__len__') else [ z0 ] * nports 
-    line = []
-    nodes = " ".join(str(i+1) for i in range(nports+1))
-    line.append(f'.SUBCKT {name} {nodes}')
+    lines = []
+    ports = list(range(1, nports+1))
+    nodes = " ".join(f"{p}" for p in ports)
+    nodes += " gnd_node"
+    lines.append(f"*\n*** Example use in SPICE:")
+    port_names = " ".join(f"Port{p}" for p in ports)
+    lines.append(f"**  X<inst> {name} {port_names} GND")
+    lines.append("")
+    lines.append(f'.SUBCKT {name} {nodes}')
+    lines.append(f"Vgnd_node_{nports+1} {nports+1} gnd_node 0")
     for i in range(nports):
-        line.append(f"R{i+1}N {    (i+1)} {dim*(i+1)  } { -z0[i].real}")
-        line.append(f"R{i+1}P {dim*(i+1)} {dim*(i+1)+1} {2*z0[i].real}")
-    line.append('')
+        lines.append(f"R{i+1}N {    (i+1)} {dim*(i+1)  } { -z0[i].real}")
+        lines.append(f"R{i+1}P {dim*(i+1)} {dim*(i+1)+1} {2*z0[i].real}")
+    lines.append('')
     for i in range(nports):
         for j in range(nports):
             index = (i * nports) + j + 1
             k = dim * (i + 1) + j + 1
             out = nports + 1 if j == nports - 1 else k + 1
-            line.append(f'A{k} %vd({dim*(j+1)} {nports+1}) %vd({k}, {out}) xfer{index}')
-            line.append(f'.model xfer{index} xfer R_I=true table=[')
+            lines.append(f'A{k} %vd({dim*(j+1)} {nports+1}) %vd({k}, {out}) xfer{index}')
+            lines.append(f'.model xfer{index} xfer R_I=true table=[')
             for n in range(len(s)):
-                line.append(f'+ {f[n]} {s[n,i,j].real} {s[n,i,j].imag}') 
-            line.append('+ ]')
-            line.append('')
-    line.append('.ENDS\n')
-    text = '\n'.join(line)
-    with open(filename, 'w') as fd:
+                lines.append(f'+ {f[n]} {s[n,i,j].real} {s[n,i,j].imag}') 
+            lines.append('+ ]')
+            lines.append('')
+    lines.append('.ENDS\n')
+    text = ""
+    if comments:
+        text += "\n".join(comments)
+        text += "\n"
+    text += '\n'.join(lines)
+    with open(filename, 'w+') as fd:
         fd.write(text) 
 
-
 if __name__ == '__main__':
-    import os
-    import sys
+    from pathlib import Path
     import skrf
     import argparse
-    parser = argparse.ArgumentParser()
-    parser.add_argument('filename', nargs=1, help='s-parameter file to validate against')
+    parser = argparse.ArgumentParser(
+        description="stospice:  A program that converts S-Parameter (*.S[234]P) files into a spice netlist .inc file")
+    parser.add_argument('filename', type=str, help='s-parameter file to convert to SPICE netlist')
+    parser.add_argument('-o', dest="overwrite",  action="store_true", help="Force overwrite exsting output", default=False)
     args = parser.parse_args()
-    filename = args.filename[0]
-    rootname = os.path.splitext(filename)[0]
-    incfile = f'{rootname}.inc'
+    filename = Path(args.filename)
+    incfile = filename.with_suffix('.inc')
+    if incfile.exists and not args.overwrite:
+        raise IOError("Output file {incfile} exists, use -o to overwrite")
     nw = skrf.Network(filename)
-    stospice(incfile, nw.name, nw.f, nw.s, nw.z0[0])
+    comments = extract_comments(filename)
+    name = nw.name
+    stospice(incfile, name, nw.f, nw.s, nw.z0[0], comments)
+    print(f"Converted {filename} to {incfile} and created SPICE sub-circuit {name}")
+
+