No such file or directory when running an ffmpeg command from script

I have been trying to run this ffmpeg command from python script to generate video of certain length from a static image but I keep getting No such file or directory error! Here is my code:

import subprocess

def generate_white_vid (duration):
    ffmpeg_create_vid_from_static_img = 'ffmpeg -loop 1 -i /same_path/WhiteBackground.jpg -c:v libx264 -t %f -pix_fmt yuv420p -vf scale=1920:1080 /same_path/white_vid2.mp4' % duration
    print ffmpeg_create_vid_from_static_img
    pp = subprocess.Popen(ffmpeg_create_vid_from_static_img)
    pp.communicate()

generate_white_vid(0.5)

However when I run the same exact command:

ffmpeg -loop 1 -i /same_path/WhiteBackground.jpg -t 0.500000 -pix_fmt yuv420p -vf scale=1920:1080 /same_path/white_vid2.mp4

from the cli, it works just fine. Where am I missing up? Here is the full trace:

Traceback (most recent call last):
  File "gen.py", line 10, in <module>
    generate_white_vid(0.5)
  File "gen.py", line 7, in generate_white_vid
    pp = subprocess.Popen(ffmpeg_create_vid_from_static_img)
  File "/home/ubuntu/anaconda2/lib/python2.7/subprocess.py", line 390, in __init__
    errread, errwrite)
  File "/home/ubuntu/anaconda2/lib/python2.7/subprocess.py", line 1024, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

When I use a list to pass the ffmpeg commands parameters as following ffmpeg_create_vid_from_static_img = ['ffmpeg', '-loop', '1', '-i', '/same_path/WhiteBackground.jpg', '-c:v', 'libx264', '-t', duration, '-pix_fmt', 'yuv420p', '-vf', 'scale=1920:1080', '/same_path/white_vid.mp4'] , I get a type error:

TypeError                                 Traceback (most recent call last)
<ipython-input-137-4a9e12e42310> in <module>()
----> 1 generate_white_vid(0.5)

<ipython-input-136-edfbfc017557> in generate_white_vid(duration)
      3     ffmpeg_create_vid_from_static_img = ['ffmpeg', '-loop', '1', '-i', '/home/ubuntu/matar/multispectral/WhiteBackground.jpg', '-c:v', 'libx264', '-t', duration, '-pix_fmt yuv420p', '-vf', 'scale=1920:1080', '/home/ubuntu/matar/multispectral/white_vid.mp4']
      4     print ffmpeg_create_vid_from_static_img
----> 5     pp = subprocess.Popen(ffmpeg_create_vid_from_static_img)
      6     pp.communicate()

/home/ubuntu/anaconda2/lib/python2.7/subprocess.pyc in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags)
    388                                 p2cread, p2cwrite,
    389                                 c2pread, c2pwrite,
--> 390                                 errread, errwrite)
    391         except Exception:
    392             # Preserve original exception in case os.close raises.

/home/ubuntu/anaconda2/lib/python2.7/subprocess.pyc in _execute_child(self, args, executable, preexec_fn, close_fds, cwd, env, universal_newlines, startupinfo, creationflags, shell, to_close, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite)
   1022                         raise
   1023                 child_exception = pickle.loads(data)
-> 1024                 raise child_exception
   1025 
   1026 

TypeError: execv() arg 2 must contain only strings