[Tkinter] tkinter - unexpected output - don't know how func is triggered before calling

[omm]

This is how my app looks like in the image below


WHAT I AM TRYING TO DO:
I am trying to create a desktop app using tkinter where I have a Entry (Textbox) to enter a module name and press on a button which calls a function that does dir(given_module_name) and displays the list in a Listbox.
Questions:
1) Somehow, when I first run my program, the Listbox is automatically being populated before pressing the button. I am not sure why this is happening.
2) When I click on the button, nothing is happening. Why

I am noob in python and I am sure I am doing something wrong somewhere but not able to figure out where.

Thanks,
Om

Here is my code:

from tkinter import *

window = Tk()
window.title("Python Help")


def lib_func(lib):
    print("Entered lib_func()----->")
    func_list = dir(lib)
    for item in func_list:
        list1.insert(END, item)
 

#lib_name="os"
#lib_funcs(lib_name)

text_label = Label(window,text="Enter lib")
text_label.grid(row=0,column=0)

str_var=StringVar()
#print("str_val type is: ",type(str_var)) #str_val type is:  <class 'tkinter.StringVar'>

# This part is confusing where the text typed in text_entry is fetched from str_val
text_entry = Entry(window,textvariable=str_var)
text_entry.grid(row=0, column=1)

list1=Listbox(window, height=30,width=35)
list1.grid(row=2,column=0,rowspan=6,columnspan=2)

enter_button = Button(window,text="Enter",command=lib_func(str_var.get()))
enter_button.grid(row=0,column=2)

window.mainloop()