Added distance calculation script.

pdb_dist.py

@@ -0,0 +1,131 @@
+#!/usr/bin/env python
+
+"""
+Calculates distances between all atoms in a structure.
+Filters the distances if a cutoff value is given (default 5.0A).
+If the cutoff is preceeded by a '+' sign, only inter-chain distances are calculated.
+
+usage: python pdb_dist.py [[-+]cutoff] <pdb file>
+example: python pdb_dist.py -5.0 1CTF.pdb
+         python pdb_dist.py +5.0 1BRS.pdb
+
+Author: {0} ({1})
+
+This program is part of the PDB tools distributed with HADDOCK
+or with the HADDOCK tutorial. The utilities in this package
+can be used to quickly manipulate PDB files, with the benefit
+of 'piping' several different commands. This is a rewrite of old
+FORTRAN77 code that was taking too much effort to compile. RIP.
+"""
+
+from __future__ import print_function
+
+import os
+import re
+import sys
+
+__author__ = "Joao Rodrigues"
+__email__ = "[email protected]"
+
+USAGE = __doc__.format(__author__, __email__)
+
+CUTOFF_DEFAULT = 5.0
+# Atom name, residue number, chain ID, same, same, same, d_ij
+_OUTPUT_FORMAT = "{0[0]:<4s} {0[1]:>3s} {0[2]:>4s} {0[3]:1s} : {1[0]:<4s} {1[1]:>4s} {1[2]:>4s} {1[3]:1s} | {2:5.2f}"
+
+def check_input(args):
+    """Checks whether to read from stdin/file and validates user input/options."""
+
+    if not len(args):
+        # From pipe
+        if not sys.stdin.isatty():
+            pdbfh = sys.stdin
+            cutoff = CUTOFF_DEFAULT
+            inter = False
+        else:
+            sys.stderr.write(USAGE)
+            sys.exit(1)
+    elif len(args) == 1:
+        # Options & Pipe _or_ file & no option
+        if re.match(r'[\-\+][0-9\.]+', args[0]):
+            inter = args[0][0] == '+'
+            cutoff = float(args[0][1:])
+            if not sys.stdin.isatty():
+                pdbfh = sys.stdin
+            else:
+                sys.stderr.write(USAGE)
+                sys.exit(1)
+        else:
+            if not os.path.isfile(args[0]):
+                sys.stderr.write('File not found: ' + args[0] + '\n')
+                sys.stderr.write(USAGE)
+                sys.exit(1)
+            pdbfh = open(args[0], 'r')
+            cutoff = CUTOFF_DEFAULT
+            inter = False
+
+    elif len(args) == 2:
+        # Option & File
+        if not re.match(r'[\-\+][0-9\.]+', args[0]):
+            sys.stderr.write('Invalid option: ' + args[0] + '\n')
+            sys.stderr.write(USAGE)
+            sys.exit(1)
+
+        if not os.path.isfile(args[1]):
+            sys.stderr.write('File not found: ' + args[1] + '\n')
+            sys.stderr.write(USAGE)
+            sys.exit(1)
+        cutoff = float(args[0][1:])
+        pdbfh = open(args[1], 'r')
+        inter = args[0][0] == '+'
+    else:
+        sys.stderr.write(USAGE)
+        sys.exit(1)
+
+    return (inter, cutoff, pdbfh)
+
+def _calculate_atom_distance(i, j):
+    """Euclidean distance between two 3d points"""
+    return ((i[0] - j[0])**2 + (i[1] - j[1])**2 + (i[2] - j[2])**2) ** 0.5
+
+def calculate_distances(fhandle, cutoff, inter):
+    """Enclosing logic in a function to speed up a bit"""
+
+    coord_re = re.compile('^(ATOM|HETATM)')
+    fhandle = fhandle
+    cutoff = cutoff
+    inter = inter
+
+    atoms = []
+    for line in fhandle:
+        line = line.strip()
+        if coord_re.match(line):
+            # atom name, altloc, res number, chain name
+            atom_uid = (line[12:16].strip(), line[17:20].strip(), line[22:26].strip(), line[21])
+            x, y, z = line[30:38], line[38:46], line[46:54]
+            x, y, z = float(x), float(y), float(z)
+
+            atoms.append((atom_uid, (x, y, z)))
+
+    for i, atom_i in enumerate(atoms):
+        for atom_j in atoms[i+1:]:
+            # Avoid intra-residue calculations & intra chain if requested
+            if not ((atom_i[0][1:] == atom_j[0][1:]) or (inter and atom_i[0][3] == atom_j[0][3])):
+                d_ij = _calculate_atom_distance(atom_i[1], atom_j[1])
+                if d_ij <= cutoff:
+                    print(_OUTPUT_FORMAT.format(atom_i[0], atom_j[0], d_ij))
+
+
+if __name__ == '__main__':
+    # Check Input
+    inter, cutoff, pdbfh = check_input(sys.argv[1:])
+
+    # Do the job
+    calculate_distances(pdbfh, cutoff, inter)
+
+    # last line of the script
+    # We can close it even if it is sys.stdin
+    pdbfh.close()
+    sys.exit(0)
+
+