Is there any way to show the dependency trees for pip packages?

You should take a look at pipdeptree:

$ pip install pipdeptree
$ pipdeptree -fl
Warning!!! Cyclic dependencies found:
------------------------------------------------------------------------
xlwt==0.7.5
ruamel.ext.rtf==0.1.1
xlrd==0.9.3
openpyxl==2.0.4
  - jdcal==1.0
pymongo==2.7.1
reportlab==3.1.8
  - Pillow==2.5.1
  - pip
  - setuptools

It doesn't generate a requirements.txt file as you indicated directly. However the source (255 lines of python code) should be relatively easy to modify to your needs, or alternatively you can (as @MERose indicated is in the pipdeptree 0.3 README ) out use:

pipdeptree --freeze  --warn silence | grep -P '^[\w0-9\-=.]+' > requirements.txt

The 0.5 version of pipdeptree also allows JSON output with the --json option, that is more easily machine parseble, at the expense of being less readable.

Warning: py2 only / abandonware

yolk can display dependencies for packages, provided that they

• were installed via setuptools

• came with metadata that includes dependency information

  $ yolk -d Theano
  Theano 0.6.0rc3
    scipy>=0.7.2
    numpy>=1.5.0