text: user12686: Suppose, I want to find the neighboring Hydrogen atoms of a specific C-alpha atom.
  The following was my effort. However, it produces a bunch of empty lists.
  from typing import List
  from Bio.PDB import Chain, Atom, NeighborSearch, PDBParser
  
  
  def get_hydrogen_atoms(c_alpha_atom):
      ns = NeighborSearch([c_alpha_atom])
      return ns.search_all(190.0, "A")
  
  p = PDBParser()
  structure = p.get_structure('16pk', '16pk.pdb')
  
  c_alpha_list = [atom for atom in structure.get_atoms()]
  
  for c_alpha in c_alpha_list:
      if c_alpha.name == "CA":
          hydrogen_list = get_hydrogen_atoms(c_alpha)
          print(hydrogen_list)
  
  How can I correct this?
  
  user10049: You posted similar question here: https://stackoverflow.com/questions/69676943/how-can-i-get-a-list-of-neighboring-hydrogen-atoms-of-an-alpha-carbon/69815509#69815509
  ok got some code :
  from Bio.PDB import Chain, Atom, NeighborSearch, PDBParser, Selection
  
  
  def get_hydrogen_atoms(c_alpha_atom: Atom.Atom, po):
      ns = NeighborSearch(po)
      return [h for h in ns.search( c_alpha_atom.get_coord(), 10.0, 'A') if h.element == 'H']
  
  p = PDBParser()
  # structure = p.get_structure('16pk', '16pk.pdb')
  structure = p.get_structure('16pk', 'pH8_5_1bq9_short.pdb')
  
  c_alpha_list = [atom for atom in structure.get_atoms() if atom.name == "CA"]
  
  print('c_alpha_list[0]  : ', c_alpha_list[0], c_alpha_list[0].id , c_alpha_list[0].get_serial_number(),'\n')
  
  po = Selection.unfold_entities(structure, 'A')
                                 
  hydrogen_list = get_hydrogen_atoms(c_alpha_list[0], po)
  
  print('hydrogen_list : \n',hydrogen_list)
  
  print('\nSelection (po) : \n', po)
  
  had to use a different PDB file because I needed the H atoms,
  pH8_5_1bq9_short.pdb :
  HETATM    1  N   FME A   1      23.447  -5.765   5.119  1.00 19.07           N
  HETATM    2  CN  FME A   1      23.308  -6.776   4.291  1.00 20.46           C
  HETATM    3  O1  FME A   1      22.504  -6.713   3.357  1.00 24.75           O
  HETATM    4  CA  FME A   1      22.488  -4.745   5.410  1.00 18.15           C
  HETATM    5  CB  FME A   1      22.433  -4.342   6.827  1.00 21.15           C
  HETATM    6  CG  FME A   1      22.198  -5.618   7.751  1.00 22.84           C
  HETATM    7  SD  FME A   1      20.445  -6.032   7.772  1.00 23.40           S
  HETATM    8  CE  FME A   1      20.476  -7.587   8.656  1.00 28.76           C
  HETATM    9  C   FME A   1      22.699  -3.530   4.487  1.00 17.12           C
  HETATM   10  O   FME A   1      23.804  -3.248   4.077  1.00 20.25           O
  HETATM    0 3HE  FME A   1      19.574  -7.938   8.726  1.00 28.76           H   new
  HETATM    0 2HG  FME A   1      22.713  -6.369   7.418  1.00 22.84           H   new
  HETATM    0 2HE  FME A   1      21.032  -8.221   8.177  1.00 28.76           H   new
  HETATM    0 2HB  FME A   1      23.260  -3.901   7.077  1.00 21.15           H   new
  HETATM    0 1HG  FME A   1      22.508  -5.438   8.652  1.00 22.84           H   new
  HETATM    0 1HE  FME A   1      20.838  -7.447   9.545  1.00 28.76           H   new
  HETATM    0 1HB  FME A   1      21.717  -3.701   6.961  1.00 21.15           H   new
  HETATM    0  HN  FME A   1      24.199  -5.711   5.532  1.00 19.07           H   new
  HETATM    0  HCN FME A   1      23.841  -7.577   4.415  1.00 20.46           H   new
  HETATM    0  HA  FME A   1      21.619  -5.138   5.231  1.00 18.15           H   new
  ATOM     11  N   ALA A   2      21.633  -2.939   4.043  1.00 15.50           N
  ATOM     12  CA  ALA A   2      21.644  -1.884   3.062  1.00 15.08           C
  ATOM     13  C   ALA A   2      20.899  -0.661   3.519  1.00 13.72           C
  ATOM     14  O   ALA A   2      20.278  -0.702   4.584  1.00 13.49           O
  ATOM     15  CB  ALA A   2      21.083  -2.339   1.710  1.00 17.86           C
  ATOM      0  H   ALA A   2      20.842  -3.144   4.312  1.00 15.50           H   new
  ATOM      0  HA  ALA A   2      22.579  -1.652   2.951  1.00 15.08           H   new
  ATOM      0  HB1 ALA A   2      21.110  -1.599   1.083  1.00 17.86           H   new
  ATOM      0  HB2 ALA A   2      21.618  -3.072   1.368  1.00 17.86           H   new
  ATOM      0  HB3 ALA A   2      20.166  -2.634   1.823  1.00 17.86           H   new
  ATOM     16  N   LYS A   3      21.005   0.412   2.774  1.00 12.48           N
  ATOM     17  CA  LYS A   3      20.341   1.658   3.029  1.00 12.61           C
  ATOM     18  C   LYS A   3      19.415   1.991   1.879  1.00 11.53           C
  ATOM     19  O   LYS A   3      19.784   1.753   0.701  1.00 11.66           O
  ATOM     20  CB  LYS A   3      21.338   2.806   3.273  1.00 13.38           C
  ATOM     21  CG  LYS A   3      22.062   2.721   4.593  1.00 16.70           C
  ATOM     22  CD  LYS A   3      23.062   3.847   4.814  1.00 18.05           C
  ATOM     23  CE  LYS A   3      23.806   3.576   6.136  1.00 20.42           C
  ATOM     24  NZ  LYS A   3      24.878   4.503   6.403  1.00 22.91           N
  ATOM      0  H   LYS A   3      21.494   0.433   2.067  1.00 12.48           H   new
  ATOM      0  HA  LYS A   3      19.821   1.557   3.842  1.00 12.61           H   new
  ATOM      0  HB2 LYS A   3      21.992   2.812   2.556  1.00 13.38           H   new
  ATOM      0  HB3 LYS A   3      20.862   3.650   3.230  1.00 13.38           H   new
  ATOM      0  HG2 LYS A   3      21.411   2.732   5.312  1.00 16.70           H   new
  ATOM      0  HG3 LYS A   3      22.527   1.871   4.644  1.00 16.70           H   new
  ATOM      0  HD2 LYS A   3      23.689   3.892   4.076  1.00 18.05           H   new
  ATOM      0  HD3 LYS A   3      22.606   4.702   4.851  1.00 18.05           H   new
  ATOM      0  HE2 LYS A   3      23.170   3.611   6.868  1.00 20.42           H   new
  ATOM      0  HE3 LYS A   3      24.166   2.676   6.116  1.00 20.42           H   new
  ATOM      0  HZ1 LYS A   3      25.266   4.294   7.176  1.00 22.91           H   new
  ATOM      0  HZ2 LYS A   3      25.479   4.458   5.748  1.00 22.91           H   new
  ATOM      0  HZ3 LYS A   3      24.551   5.330   6.449  1.00 22.91           H   new
  ATOM     25  N   TRP A   4      18.274   2.598   2.165  1.00 10.75           N
  ATOM     26  CA  TRP A   4      17.283   3.019   1.181  1.00 10.69           C
  ATOM     27  C   TRP A   4      16.875   4.472   1.502  1.00 11.37           C
  ATOM     28  O   TRP A   4      16.812   4.872   2.651  1.00 17.19           O
  ATOM     29  CB  TRP A   4      16.012   2.143   1.352  1.00 11.20           C
  ATOM     30  CG  TRP A   4      16.164   0.734   0.997  1.00 11.80           C
  ATOM     31  CD1 TRP A   4      16.913  -0.218   1.669  1.00 12.50           C
  ATOM     32  CD2 TRP A   4      15.535   0.036  -0.079  1.00 11.53           C
  ATOM     33  NE1 TRP A   4      16.806  -1.435   1.050  1.00 12.76           N
  ATOM     34  CE2 TRP A   4      15.959  -1.302  -0.013  1.00 12.61           C
  ATOM     35  CE3 TRP A   4      14.642   0.421  -1.079  1.00 11.88           C
  ATOM     36  CZ2 TRP A   4      15.531  -2.258  -0.929  1.00 13.18           C
  ATOM     37  CZ3 TRP A   4      14.217  -0.527  -1.989  1.00 12.54           C
  ATOM     38  CH2 TRP A   4      14.668  -1.858  -1.894  1.00 14.26           C
  
  output :
  c_alpha_list[0]  :  <Atom CA> CA 4 
  
  hydrogen_list : 
   [<Atom HB1>, <Atom HB3>, <Atom H>, <Atom 2HE>, <Atom 3HE>, <Atom 1HE>, <Atom HB3>, <Atom HA>, <Atom HG2>, <Atom HB2>, <Atom HCN>, <Atom HA>, <Atom HN>, <Atom 1HB>, <Atom 2HB>, <Atom 2HG>, <Atom 1HG>, <Atom H>, <Atom HB2>, <Atom HA>, <Atom HD2>, <Atom HG3>, <Atom HD3>, <Atom HZ2>, <Atom HE3>, <Atom HE2>, <Atom HZ1>]
  
  Selection (po) : 
   [<Atom N>, <Atom CN>, <Atom O1>, <Atom CA>, <Atom CB>, <Atom CG>, <Atom SD>, <Atom CE>, <Atom C>, <Atom O>, <Atom 3HE>, <Atom 2HG>, <Atom 2HE>, <Atom 2HB>, <Atom 1HG>, <Atom 1HE>, <Atom 1HB>, <Atom HN>, <Atom HCN>, <Atom HA>, <Atom N>, <Atom CA>, <Atom C>, <Atom O>, <Atom CB>, <Atom H>, <Atom HA>, <Atom HB1>, <Atom HB2>, <Atom HB3>, <Atom N>, <Atom CA>, <Atom C>, <Atom O>, <Atom CB>, <Atom CG>, <Atom CD>, <Atom CE>, <Atom NZ>, <Atom H>, <Atom HA>, <Atom HB2>, <Atom HB3>, <Atom HG2>, <Atom HG3>, <Atom HD2>, <Atom HD3>, <Atom HE2>, <Atom HE3>, <Atom HZ1>, <Atom HZ2>, <Atom HZ3>, <Atom N>, <Atom CA>, <Atom C>, <Atom O>, <Atom CB>, <Atom CG>, <Atom CD1>, <Atom CD2>, <Atom NE1>, <Atom CE2>, <Atom CE3>, <Atom CZ2>, <Atom CZ3>, <Atom CH2>]
  
  the selection list contains both ATOM and HETATM
  have a look at : https://www.biostars.org/p/269579/ How to use biopython neighborsearch?
  and Bio.PDB.NeighborSearch module :https://biopython.org/docs/1.75/api/Bio.PDB.NeighborSearch.html ;
  Bio.PDB.Atom module :https://biopython.org/docs/1.75/api/Bio.PDB.Atom.html
  
original_text: 12686: <p>Suppose, I want to find the neighboring Hydrogen atoms of a specific C-alpha atom.</p>
  <p>The following was my effort. However, it produces a bunch of empty lists.</p>
  <pre><code>from typing import List
  from Bio.PDB import Chain, Atom, NeighborSearch, PDBParser
  
  
  def get_hydrogen_atoms(c_alpha_atom):
      ns = NeighborSearch([c_alpha_atom])
      return ns.search_all(190.0, &quot;A&quot;)
  
  p = PDBParser()
  structure = p.get_structure('16pk', '16pk.pdb')
  
  c_alpha_list = [atom for atom in structure.get_atoms()]
  
  for c_alpha in c_alpha_list:
      if c_alpha.name == &quot;CA&quot;:
          hydrogen_list = get_hydrogen_atoms(c_alpha)
          print(hydrogen_list)
  </code></pre>
  <p>How can I correct this?</p>
   10049: <p>You posted similar question here: <a href="https://stackoverflow.com/questions/69676943/how-can-i-get-a-list-of-neighboring-hydrogen-atoms-of-an-alpha-carbon/69815509#69815509">https://stackoverflow.com/questions/69676943/how-can-i-get-a-list-of-neighboring-hydrogen-atoms-of-an-alpha-carbon/69815509#69815509</a></p>
  <p>ok got some code :</p>
  <pre><code>from Bio.PDB import Chain, Atom, NeighborSearch, PDBParser, Selection
  
  
  def get_hydrogen_atoms(c_alpha_atom: Atom.Atom, po):
      ns = NeighborSearch(po)
      return [h for h in ns.search( c_alpha_atom.get_coord(), 10.0, 'A') if h.element == 'H']
  
  p = PDBParser()
  # structure = p.get_structure('16pk', '16pk.pdb')
  structure = p.get_structure('16pk', 'pH8_5_1bq9_short.pdb')
  
  c_alpha_list = [atom for atom in structure.get_atoms() if atom.name == &quot;CA&quot;]
  
  print('c_alpha_list[0]  : ', c_alpha_list[0], c_alpha_list[0].id , c_alpha_list[0].get_serial_number(),'\n')
  
  po = Selection.unfold_entities(structure, 'A')
                                 
  hydrogen_list = get_hydrogen_atoms(c_alpha_list[0], po)
  
  print('hydrogen_list : \n',hydrogen_list)
  
  print('\nSelection (po) : \n', po)
  </code></pre>
  <p>had to use a different PDB file because I needed the H atoms,</p>
  <p>pH8_5_1bq9_short.pdb :</p>
  <pre><code>HETATM    1  N   FME A   1      23.447  -5.765   5.119  1.00 19.07           N
  HETATM    2  CN  FME A   1      23.308  -6.776   4.291  1.00 20.46           C
  HETATM    3  O1  FME A   1      22.504  -6.713   3.357  1.00 24.75           O
  HETATM    4  CA  FME A   1      22.488  -4.745   5.410  1.00 18.15           C
  HETATM    5  CB  FME A   1      22.433  -4.342   6.827  1.00 21.15           C
  HETATM    6  CG  FME A   1      22.198  -5.618   7.751  1.00 22.84           C
  HETATM    7  SD  FME A   1      20.445  -6.032   7.772  1.00 23.40           S
  HETATM    8  CE  FME A   1      20.476  -7.587   8.656  1.00 28.76           C
  HETATM    9  C   FME A   1      22.699  -3.530   4.487  1.00 17.12           C
  HETATM   10  O   FME A   1      23.804  -3.248   4.077  1.00 20.25           O
  HETATM    0 3HE  FME A   1      19.574  -7.938   8.726  1.00 28.76           H   new
  HETATM    0 2HG  FME A   1      22.713  -6.369   7.418  1.00 22.84           H   new
  HETATM    0 2HE  FME A   1      21.032  -8.221   8.177  1.00 28.76           H   new
  HETATM    0 2HB  FME A   1      23.260  -3.901   7.077  1.00 21.15           H   new
  HETATM    0 1HG  FME A   1      22.508  -5.438   8.652  1.00 22.84           H   new
  HETATM    0 1HE  FME A   1      20.838  -7.447   9.545  1.00 28.76           H   new
  HETATM    0 1HB  FME A   1      21.717  -3.701   6.961  1.00 21.15           H   new
  HETATM    0  HN  FME A   1      24.199  -5.711   5.532  1.00 19.07           H   new
  HETATM    0  HCN FME A   1      23.841  -7.577   4.415  1.00 20.46           H   new
  HETATM    0  HA  FME A   1      21.619  -5.138   5.231  1.00 18.15           H   new
  ATOM     11  N   ALA A   2      21.633  -2.939   4.043  1.00 15.50           N
  ATOM     12  CA  ALA A   2      21.644  -1.884   3.062  1.00 15.08           C
  ATOM     13  C   ALA A   2      20.899  -0.661   3.519  1.00 13.72           C
  ATOM     14  O   ALA A   2      20.278  -0.702   4.584  1.00 13.49           O
  ATOM     15  CB  ALA A   2      21.083  -2.339   1.710  1.00 17.86           C
  ATOM      0  H   ALA A   2      20.842  -3.144   4.312  1.00 15.50           H   new
  ATOM      0  HA  ALA A   2      22.579  -1.652   2.951  1.00 15.08           H   new
  ATOM      0  HB1 ALA A   2      21.110  -1.599   1.083  1.00 17.86           H   new
  ATOM      0  HB2 ALA A   2      21.618  -3.072   1.368  1.00 17.86           H   new
  ATOM      0  HB3 ALA A   2      20.166  -2.634   1.823  1.00 17.86           H   new
  ATOM     16  N   LYS A   3      21.005   0.412   2.774  1.00 12.48           N
  ATOM     17  CA  LYS A   3      20.341   1.658   3.029  1.00 12.61           C
  ATOM     18  C   LYS A   3      19.415   1.991   1.879  1.00 11.53           C
  ATOM     19  O   LYS A   3      19.784   1.753   0.701  1.00 11.66           O
  ATOM     20  CB  LYS A   3      21.338   2.806   3.273  1.00 13.38           C
  ATOM     21  CG  LYS A   3      22.062   2.721   4.593  1.00 16.70           C
  ATOM     22  CD  LYS A   3      23.062   3.847   4.814  1.00 18.05           C
  ATOM     23  CE  LYS A   3      23.806   3.576   6.136  1.00 20.42           C
  ATOM     24  NZ  LYS A   3      24.878   4.503   6.403  1.00 22.91           N
  ATOM      0  H   LYS A   3      21.494   0.433   2.067  1.00 12.48           H   new
  ATOM      0  HA  LYS A   3      19.821   1.557   3.842  1.00 12.61           H   new
  ATOM      0  HB2 LYS A   3      21.992   2.812   2.556  1.00 13.38           H   new
  ATOM      0  HB3 LYS A   3      20.862   3.650   3.230  1.00 13.38           H   new
  ATOM      0  HG2 LYS A   3      21.411   2.732   5.312  1.00 16.70           H   new
  ATOM      0  HG3 LYS A   3      22.527   1.871   4.644  1.00 16.70           H   new
  ATOM      0  HD2 LYS A   3      23.689   3.892   4.076  1.00 18.05           H   new
  ATOM      0  HD3 LYS A   3      22.606   4.702   4.851  1.00 18.05           H   new
  ATOM      0  HE2 LYS A   3      23.170   3.611   6.868  1.00 20.42           H   new
  ATOM      0  HE3 LYS A   3      24.166   2.676   6.116  1.00 20.42           H   new
  ATOM      0  HZ1 LYS A   3      25.266   4.294   7.176  1.00 22.91           H   new
  ATOM      0  HZ2 LYS A   3      25.479   4.458   5.748  1.00 22.91           H   new
  ATOM      0  HZ3 LYS A   3      24.551   5.330   6.449  1.00 22.91           H   new
  ATOM     25  N   TRP A   4      18.274   2.598   2.165  1.00 10.75           N
  ATOM     26  CA  TRP A   4      17.283   3.019   1.181  1.00 10.69           C
  ATOM     27  C   TRP A   4      16.875   4.472   1.502  1.00 11.37           C
  ATOM     28  O   TRP A   4      16.812   4.872   2.651  1.00 17.19           O
  ATOM     29  CB  TRP A   4      16.012   2.143   1.352  1.00 11.20           C
  ATOM     30  CG  TRP A   4      16.164   0.734   0.997  1.00 11.80           C
  ATOM     31  CD1 TRP A   4      16.913  -0.218   1.669  1.00 12.50           C
  ATOM     32  CD2 TRP A   4      15.535   0.036  -0.079  1.00 11.53           C
  ATOM     33  NE1 TRP A   4      16.806  -1.435   1.050  1.00 12.76           N
  ATOM     34  CE2 TRP A   4      15.959  -1.302  -0.013  1.00 12.61           C
  ATOM     35  CE3 TRP A   4      14.642   0.421  -1.079  1.00 11.88           C
  ATOM     36  CZ2 TRP A   4      15.531  -2.258  -0.929  1.00 13.18           C
  ATOM     37  CZ3 TRP A   4      14.217  -0.527  -1.989  1.00 12.54           C
  ATOM     38  CH2 TRP A   4      14.668  -1.858  -1.894  1.00 14.26           C
  </code></pre>
  <p>output :</p>
  <pre><code>c_alpha_list[0]  :  &lt;Atom CA&gt; CA 4 
  
  hydrogen_list : 
   [&lt;Atom HB1&gt;, &lt;Atom HB3&gt;, &lt;Atom H&gt;, &lt;Atom 2HE&gt;, &lt;Atom 3HE&gt;, &lt;Atom 1HE&gt;, &lt;Atom HB3&gt;, &lt;Atom HA&gt;, &lt;Atom HG2&gt;, &lt;Atom HB2&gt;, &lt;Atom HCN&gt;, &lt;Atom HA&gt;, &lt;Atom HN&gt;, &lt;Atom 1HB&gt;, &lt;Atom 2HB&gt;, &lt;Atom 2HG&gt;, &lt;Atom 1HG&gt;, &lt;Atom H&gt;, &lt;Atom HB2&gt;, &lt;Atom HA&gt;, &lt;Atom HD2&gt;, &lt;Atom HG3&gt;, &lt;Atom HD3&gt;, &lt;Atom HZ2&gt;, &lt;Atom HE3&gt;, &lt;Atom HE2&gt;, &lt;Atom HZ1&gt;]
  
  Selection (po) : 
   [&lt;Atom N&gt;, &lt;Atom CN&gt;, &lt;Atom O1&gt;, &lt;Atom CA&gt;, &lt;Atom CB&gt;, &lt;Atom CG&gt;, &lt;Atom SD&gt;, &lt;Atom CE&gt;, &lt;Atom C&gt;, &lt;Atom O&gt;, &lt;Atom 3HE&gt;, &lt;Atom 2HG&gt;, &lt;Atom 2HE&gt;, &lt;Atom 2HB&gt;, &lt;Atom 1HG&gt;, &lt;Atom 1HE&gt;, &lt;Atom 1HB&gt;, &lt;Atom HN&gt;, &lt;Atom HCN&gt;, &lt;Atom HA&gt;, &lt;Atom N&gt;, &lt;Atom CA&gt;, &lt;Atom C&gt;, &lt;Atom O&gt;, &lt;Atom CB&gt;, &lt;Atom H&gt;, &lt;Atom HA&gt;, &lt;Atom HB1&gt;, &lt;Atom HB2&gt;, &lt;Atom HB3&gt;, &lt;Atom N&gt;, &lt;Atom CA&gt;, &lt;Atom C&gt;, &lt;Atom O&gt;, &lt;Atom CB&gt;, &lt;Atom CG&gt;, &lt;Atom CD&gt;, &lt;Atom CE&gt;, &lt;Atom NZ&gt;, &lt;Atom H&gt;, &lt;Atom HA&gt;, &lt;Atom HB2&gt;, &lt;Atom HB3&gt;, &lt;Atom HG2&gt;, &lt;Atom HG3&gt;, &lt;Atom HD2&gt;, &lt;Atom HD3&gt;, &lt;Atom HE2&gt;, &lt;Atom HE3&gt;, &lt;Atom HZ1&gt;, &lt;Atom HZ2&gt;, &lt;Atom HZ3&gt;, &lt;Atom N&gt;, &lt;Atom CA&gt;, &lt;Atom C&gt;, &lt;Atom O&gt;, &lt;Atom CB&gt;, &lt;Atom CG&gt;, &lt;Atom CD1&gt;, &lt;Atom CD2&gt;, &lt;Atom NE1&gt;, &lt;Atom CE2&gt;, &lt;Atom CE3&gt;, &lt;Atom CZ2&gt;, &lt;Atom CZ3&gt;, &lt;Atom CH2&gt;]
  </code></pre>
  <p>the selection list contains both ATOM and HETATM</p>
  <p>have a look at : <a href="https://www.biostars.org/p/269579/" rel="nofollow noreferrer">https://www.biostars.org/p/269579/</a> How to use biopython neighborsearch?</p>
  <p>and Bio.PDB.NeighborSearch module :<a href="https://biopython.org/docs/1.75/api/Bio.PDB.NeighborSearch.html" rel="nofollow noreferrer">https://biopython.org/docs/1.75/api/Bio.PDB.NeighborSearch.html</a> ;</p>
  <p>Bio.PDB.Atom module :<a href="https://biopython.org/docs/1.75/api/Bio.PDB.Atom.html" rel="nofollow noreferrer">https://biopython.org/docs/1.75/api/Bio.PDB.Atom.html</a></p>
  