nothing appears in the output

### Describe the error
running any of the followings:
manimgl code.py
or
manim-render code.py
will give no output and terminals goes to halt state (the curser just blinks)
### Code and Error
**Code**:
manimgl code.py Scene flags

**Error**:
nothing appears in the output, the curser just blinks

### Environment
**OS System**: Ubuntu 20
**manim version**: master
conda list:
Name Version Build Channel
_libgcc_mutex 0.1 main
argparse 1.4.0 pypi_0 pypi
backcall 0.2.0 pypi_0 pypi
ca-certificates 2021.1.19 h06a4308_0
certifi 2020.12.5 py38h06a4308_0
colour 0.1.5 pypi_0 pypi
cycler 0.10.0 pypi_0 pypi
decorator 4.4.2 pypi_0 pypi
glcontext 2.3.2 pypi_0 pypi
ipython 7.20.0 pypi_0 pypi
ipython-genutils 0.2.0 pypi_0 pypi
jedi 0.18.0 pypi_0 pypi
kiwisolver 1.3.1 pypi_0 pypi
ld_impl_linux-64 2.33.1 h53a641e_7
libedit 3.1.20191231 h14c3975_1
libffi 3.3 he6710b0_2
libgcc-ng 9.1.0 hdf63c60_0
libstdcxx-ng 9.1.0 hdf63c60_0
manimgl 1.0.1.dev2 dev_0
manimpango 0.2.3 pypi_0 pypi
mapbox-earcut 0.12.10 pypi_0 pypi
matplotlib 3.3.4 pypi_0 pypi
moderngl 5.6.3 pypi_0 pypi
moderngl-window 2.3.0 pypi_0 pypi
mpmath 1.2.1 pypi_0 pypi
multipledispatch 0.6.0 pypi_0 pypi
ncurses 6.2 he6710b0_1
numpy 1.20.1 pypi_0 pypi
openssl 1.1.1i h27cfd23_0
parso 0.8.1 pypi_0 pypi
pexpect 4.8.0 pypi_0 pypi
pickleshare 0.7.5 pypi_0 pypi
pillow 8.1.0 pypi_0 pypi
pip 20.3.3 py38h06a4308_0
progressbar 2.5 pypi_0 pypi
prompt-toolkit 3.0.16 pypi_0 pypi
ptyprocess 0.7.0 pypi_0 pypi
pydub 0.24.1 pypi_0 pypi
pyglet 1.5.15 pypi_0 pypi
pygments 2.8.0 pypi_0 pypi
pyopengl 3.1.5 pypi_0 pypi
pyparsing 2.4.7 pypi_0 pypi
pyrr 0.10.3 pypi_0 pypi
python 3.8.5 h7579374_1
python-dateutil 2.8.1 pypi_0 pypi
pyyaml 5.4.1 pypi_0 pypi
readline 8.1 h27cfd23_0
scipy 1.6.1 pypi_0 pypi
screeninfo 0.6.7 pypi_0 pypi
setuptools 52.0.0 py38h06a4308_0
six 1.15.0 pypi_0 pypi
sqlite 3.33.0 h62c20be_0
sympy 1.7.1 pypi_0 pypi
tk 8.6.10 hbc83047_0
tqdm 4.57.0 pypi_0 pypi
traitlets 5.0.5 pypi_0 pypi
validators 0.18.2 pypi_0 pypi
wcwidth 0.2.5 pypi_0 pypi
wheel 0.36.2 pyhd3eb1b0_0
xz 5.2.5 h7b6447c_0
zlib 1.2.11 h7b6447c_3