diff --git a/nibabel/cmdline/parrec2nii.py b/nibabel/cmdline/parrec2nii.py
index 0ae6b3fb4..aa8861042 100644
--- a/nibabel/cmdline/parrec2nii.py
+++ b/nibabel/cmdline/parrec2nii.py
@@ -358,8 +358,7 @@ def proc_file(infile, opts):
             )
             with open(basefilename + '.bvals', 'w') as fid:
                 # np.savetxt could do this, but it's just a loop anyway
-                for val in bvals:
-                    fid.write(f'{val} ')
+                fid.write(' '.join(str(val) for val in bvals) + ' ')
                 fid.write('\n')
         else:
             verbose('Writing .bvals and .bvecs files')
@@ -369,13 +368,11 @@ def proc_file(infile, opts):
             bvecs = apply_affine(bv_reorient, bvecs)
             with open(basefilename + '.bvals', 'w') as fid:
                 # np.savetxt could do this, but it's just a loop anyway
-                for val in bvals:
-                    fid.write(f'{val} ')
+                fid.write(' '.join(str(val) for val in bvals) + ' ')
                 fid.write('\n')
             with open(basefilename + '.bvecs', 'w') as fid:
                 for row in bvecs.T:
-                    for val in row:
-                        fid.write(f'{val} ')
+                    fid.write(' '.join(str(val) for val in row) + ' ')
                     fid.write('\n')
 
     # export data labels varying along the 4th dimensions if requested
diff --git a/nibabel/volumeutils.py b/nibabel/volumeutils.py
index 41bff7275..c5ebbdd2c 100644
--- a/nibabel/volumeutils.py
+++ b/nibabel/volumeutils.py
@@ -830,8 +830,7 @@ def write_zeros(fileobj: io.IOBase, count: int, block_size: int = 8194) -> None:
     nblocks = int(count // block_size)
     rem = count % block_size
     blk = b'\x00' * block_size
-    for bno in range(nblocks):
-        fileobj.write(blk)
+    fileobj.write(blk * nblocks)
     fileobj.write(b'\x00' * rem)